Modifiability is a common quality attribute scenario. From these considerations we can see the portions of the performance general scenario, an example of which is shown in Figure 4.5: "Users initiate 1,000 transactions per minute stochastically under normal operations, and these transactions are processed with an average latency of two seconds.". Architecture Level Modifiability Analysis (ALMA) deals with change scenarios to analyze the modifi-ability of an application system [3]. For example, a modifiability general scenario is: The platform on which the system depends is changed. Stimulus. General scenarios provide a framework for generating a large number of generic, system-independent, quality-attribute-specific scenarios. Integrity is the property that data or services are being delivered as intended. And it supports a broad range of air quality monitoring devices. 3. system is … Stimulus: event. Smart transportation systems or intelligent energy management could remain operational for 20 years or more. We will also study the different dimensions of modifiability by answering the question, who or what can change. Sad to say, these researchers were Bass, Clements, and Kazman, and the book was the first edition of Software Architecture in Practice. The response measure can specify an availability percentage, or it can specify a time to repair, times during which the system must be available, or the duration for which the system must be available. Artifact 4. • Source ofstimulus. - In Figure 4.3, the stimulus is that an unanticipated message arrives. In our example, the unexpected message arrives from outside the system. • A QAS is a quality-attribute-specific requirement, that consists of: 1. One of the things that make performance complicated is the number of event sources and arrival patterns. Events (interrupts, messages, requests from users, or the passage of time) occur, and the system must respond to them. Now it's the need for personalization and customization is an additional driver for the support of modifiability by the end user. The system can be in various operational modes, such as normal, emergency, or overload. There are a number of possible reactions to a system failure. Response. However, in many situations, other people involved in a software system can also make modifications. And finally, the dynamic nature and the long system life-cycle of Internet of Things systems will have to lead to adaptive architecture that need to support runtime modifiability and dynamic compositions. Response. In the first week, you'll discover why having a well-designed architecture is important and which challenges you might come across while developing your architecture. An end user changing the screen saver is clearly making a change to one of the aspects of the system. Could be an actor, an actuator, a sensor, and so on. And the total effort for implementing it should be less than 20 days. This includes evolving, changing, and updating the system. When is the change made and who makes it (the environment)? Analysis, architecture, design, class, subsystem integration completed; system delivered, Piece of design, piece of code, complete application, At design time, at development time, at compile time, at deployment time, Provides access to state values; provides computed values; prepares test environment, Length of longest dependency chain in a test, Length of time to prepare test environment. If the only goal were to prevent access to a system, disallowing all access would be an effective defensive measure. System failure means … when the system does not provide the service for which it was intended. When is the change made and who makes it? The paper addresses and analyzes the internal potential problems due to modifiability using scenario-based analysis. And this will really allow us to compete for services in the environmental monitoring area. In Figure 4.6, an audit trail is maintained. The source of the attack may be either a human or another system. So ISO 9126, the software engineering product quality standards, includes the following definition related to modifying systems. The user actions with which usability is concerned always occur at runtime or at system configuration time. Artifact. Changes can be made to the implementation (by modifying the source code), during compile (using compile-time switches), during build (by choice of libraries), during configuration setup (by a range of techniques, including parameter setting) or during execution (by parameter setting). In our example, the transactions should be processed with an average latency of two seconds. The system must process the arriving events. We cannot give the relations among stimuli in a general way because they depend partially on environment. Reveals the driving quality attribute requirements of a software- intensive system • scenario based . (typically performance, modifiability, security, and availability) Scenarios are the leaves Output: a characterization and prioritization of specific quality attribute requirements. And this will be the subject of our diamond case study. In the example, the scenario is violated since the change cannot … Source of stimulus. Portions of the code, the design, or the complete system may be tested. Aqualityattributescenarioisaquality-attribute-specificrequirement.Itconsistsofsixparts. Each of these security categories gives rise to a collection of general scenarios. Response. A change can be the addition of a function, the modification of an existing function, or the deletion of a function. Changes used to be made to source code by a developer and were deployed in the next release. This is some entity (a human, a computer system, or any Figure 4.7 is an example of a testability scenario concerning the performance of a unit test: A unit tester performs a unit test on a completed system component that provides an interface for controlling its behavior and observing its output; 85% path coverage is achieved within three hours. Now this brings us to the general scenario for modifiability. So we define modifiability as the ease with which it can be modified to changes in the environment, requirements or functional specification without introducing defects or degrading existing qualities. The quality attributes provide the means for measuring the fitness and suitability of a product. The target of the attack can be either the services of the system or the data within it. This might be the completion of an analysis or design increment, the completion of a coding increment such as a class, the completed integration of a subsystem, or the completion of the whole system. Well, several studies have shown that 50 to 70% of the total life-cycle cost of a software system is spent after the system has been built. Well, several studies have shown that 50 to 70% of the total life-cycle cost of a software system is spent after the system has been built. The difficulty with security is allowing access to legitimate users and determining legitimacy. An audit trail is also useful in correcting from a successful attack. In our example, the testing is performed by a tester. The category of platform changes is also called portability. It can also be made to the qualities of the system-making it more responsive, increasing its availability, and so forth. An example of an availability general scenario appeared in Figure 4.3. Response. When is the change made and who makes it (the environment). Performance is not a common quality attribute scenario. The response is measured by task time, number of errors, number of problems solved, user satisfaction, gain of user knowledge, ratio of successful operations to total operations, or amount of time/data lost when an error occurs. To view this video please enable JavaScript, and consider upgrading to a web browser that Table 4.2 presents the possible values for each portion of a modifiability scenario. sequences of events, and assess their impact on the system. Now the environment section of the scenario specifies when the change will happen, while the response consist in actually making the changes, testing it, and deploying it. Stimulus. A quality attribute scenario has six parts, shown in the schematic: Source of Stimulus: the entity generating the stimulus. Environment. Equally clear, it is not in the same category as changing the system so that it can be used over the Web rather than on a single machine. And response measure quantifies the impact of the change in terms of number of modified artifacts, the cost, time, and the number of new defects introduced. This portion specifies what is to be changed-the functionality of a system, its platform, its user interface, its environment, or another system with which it interoperates. And it can change capacity, like the number of users supported and the number of simultaneous operations. a human or computer system 2. Now, ISO 25010 adds the dimension of quality by stating modifiability is a degree to which a system can be modified without introducing defects or degrading existing quality. An arrival pattern for events may be characterized as either periodic or stochastic. A quality attribute scenario is a quality-attribute-specific requirement. Table 4.3 gives elements of the general scenarios that characterize performance. General scenarios provide a framework for generating a large number of generic, system-independent, quality-attribute-specific scenarios. true. In each case, the pattern of events arriving and the pattern of responses can be characterized, and this characterization forms the language with which to construct general performance scenarios. This may be a brief delay in the response time or it may be the time it takes someone to fly to a remote location in the mountains of Peru to repair a piece of mining machinery (this example was given by a person who was responsible for repairing the software in a mining machine engine.). Assurance is the property that the parties to a transaction are who they purport to be. Most commonly in the past, a change was made to source code. This means that a hacker cannot access your income tax returns on a government computer. Table 4.1 presents the possible values for each portion of an availability scenario. Quality attribute scenarios 1. Response measure. The arrival pattern can be characterized as periodic, stochastic, or sporadic. Artifact. And Google's new modular phone, Ara, is an extreme example of modifiability by the end user. In the third and fourth week, you will learn how to correctly write quality attributes and quality attribute scenarios for a specific case. In our example, the system should notify the operator of the unexpected message and continue to operate normally. The availability of a system is the probability that it will be operational when it is needed. Stimulus. We use a common form to specify all quality attribute requirements. This may be as simple as a playback capability for data recorded across various interfaces or as complicated as a testing chamber for an engine. The testing is performed by unit testers, integration testers, system testers, or the client. Lastly, you'll come to understand the business impact of the technical decisions that you make as an IoT system architect. This means that, when a customer sends a credit card number to an Internet merchant, the merchant is who the customer thinks they are. Still, the intervening years have done nothing to lessen the basic truth of the strong relationship between architectural quality and system quality. In Figure 4.3, there is no downtime as a result of the unexpected message. Stimulus. For the Web-based financial system, the response might be the number of transactions that can be processed in a minute. Thus, the system must authorize legitimate users and grant them access to data and services, at the same time rejecting unauthorized users, denying them access, and reporting unauthorized access. Frequently this is done through use of a test harness, specialized software designed to exercise the software under test. What can change (the artifact)? It includes provisioning the device, device data in the database and running field tests. Tesla owners should get software updates every few weeks that provide new features. The source tells us who will make the change, while the stimulus describes what will change. A system failure occurs when the system no longer delivers a service consistent with its specification. This includes evolving, changing, and updating the system. The component that generated the message did so at a different time than expected. Sometimes the category of platform changes is also called portability. Availability is concerned with system failure and duration of system failures. It has the disadvantage of occasionally being a force-fit for some aspects of quality attributes. One, maintainability is the capability of the software to be modified. Some stimuli occur during runtime and others occur before. This is some entity (a human, a computer system, or any We also realize that many new vendors are entering these markets. The portions of the usability general scenarios are: Source of stimulus. Environment. Modifiability is about the cost of change, both in time and money. And this brings up a number of concerns like what can change? Stimulus. System-specific scenarios can be used to more clearly describe the quality attributes that are important to the system and what the desired quality attribute responses should be. Up till now, we have been talking about quality in an informal way. quality attributes to evaluate, scenarios to test the quality attributes and finally to estimate the degree to which the architecture provides the support [9]. However, today the question of when a change is made is intertwined with the question of who makes it. Now, modifiability also has a big impact on the competitiveness of our business because it determines the efforts to produce the next release, and it will shorten the time to market for releasing new features with less cost. This is some entity (a human, a computer system, or any other actuator) that generated the stimulus. A senior software engineer will add support for a new type of monitoring device, the noise monitor. In our example, the modification is made with no side effects. Source of stimulus. The modifiability quality is concerned with what can change, when are changes made, and who makes the changes. In our example, the audit trail allows the accounts from which money was embezzled to be restored to their original state. I highly recommend this course with people who are software architects and who intended to become one day. In fact, all of the evidence points squarely in its favor, and usability has proven to be no exception. For most of the history of software engineering, performance has been the driving factor in system architecture. If the user is unfamiliar with a particular system or a particular aspect of it, what can the system do to make the task of learning easier? Any action that occurs before then is performed by developers and, although a user may also be the developer, we distinguish between these roles even if performed by the same person. 2. Software Architecture, Architectural Pattern, Non-Functional Requirement, Software Requirements. Modifiability is clearly a design quality attribute but can be addressed during different phases of the life-cycle. In software architecture analysis of modifiability, we are not concerned with changes that occurred in the past. Quality Attribute Scenarios [BCK03] ... Modifiability Scenarios Cost in effort, money, time, extent affects other system functions or qualities Measure Locate places in architecture for modifying, modify, test modification, deploys modification Response For example, it may occur with an exchange of severalmessages between a client and a server (culminating in an unexpected message), each of which is an atomic event from a performance perspective. Once a change has been specified, the new implementation must be designed, implemented, tested, and deployed. Modifiability is a design quality that can be supported by mechanisms throughout all the phases in the system life-cycle. The domain specific, or general quality attribute scenario. One such technique is quality-attribute-scenario analysis, which captures architecturally focused requirements from stakeholders. Environment. Notice that this formulation does not consider whether the system is networked or standalone. Figure 4.6 presents an example. It brings up two concerns. Response. QUALITY ATTRIBUTE SCENARIOS A quality attribute scenario is a quality-attribute-specific requirement. Satisfying the request requires resources to be consumed. abstract quality goal of modifiability must be made concrete. omission, crash, timing, response, System's processors, communication channels, persistent storage, processes, degraded mode (i.e., fewer features, a fall back solution). A quality attribute (QA) is a measurable or testable property of a system that is used to indicate how well the system satisfies the needs of its stakeholders.In other words, a quality attribute (aka as Non-Functional Requirements) is what makes a system good with respect to a specific stakeholder.An example of a QA is how fast the function must be performed or how resilient it must be … The stimuli are the event arrivals. The stimulus is an attack or an attempt to break security. And woe to the architect (or architecture writer!) A modifiable architecture also creates opportunities for building reusable components and can simplify maintenance because small components are less complex and, if well designed, have fewer dependencies on other components. What does the system do to give the user confidence that the correct action is being taken? The scenarios are the most important part of the utility tree, the main reason is that the scenarios help us understand the quality attributes needed, and more importantly, by tying the attributes to real instances in the system the scenarios help make these goals both concrete and measurable. true. In our example, the transactions are processed. And again, this is comparable with the complexity of avionics. Periodic event arrival is most often seen in real-time systems. In the last five years, our understanding of the relation between usability and software architecture has deepened (see the sidebar Usability Mea Culpa). Those changes may be to add, delete, or modify any one of these aspects. A change can occur to any aspect of a system, most commonly the functions that the system computes, the platform the system exists on (the hardware, operating system, middleware, etc. After this module you should be able to formulate your own quality requirements. Functional requirements are expressed as use cases, and quality attributes are expressed as quality attribute scenarios templates (stimulus-response) ( Bardram et al., 2005 ). The capacity of the system may also change. A sample modifiability scenario is "A developer wishes to change the user interface to make a screen's background color blue. The stimulus is that the end user wishes to use a system efficiently, learn to use the system, minimize the impact of errors, adapt the system, or feel comfortable with the system. Facilitating this kind of understanding aids discussions of architectural decisions, particularly about tradeoffs. The later a problem is discovered and the deeper into the architecture its repair must be made, the more the repair is threatened by time and budget pressures. So let's focus on the modifiability scenario for adding a new device type. Table 4.5 gives the testability general scenario generation table. System should detect event and do one or more of the following: notify appropriate parties, including the user and other systems, disable sources of events that cause fault or failure according to defined rules, be unavailable for a prespecified interval, where interval depends on criticality of system, continue to operate in normal or degraded mode, Time interval when the system must be available, Time interval in which system can be in degraded mode. Not only does the system need to provide access to legitimate users, but it needs to support the granting or withdrawing of access. Availability is the property that the system will be available for legitimate use. The same system that has to support a new browser may also have to support a new media type. In our example, the system is in normal mode. And now we want to add the support for noise monitoring. Software Quality Attributes are the benchmarks that describe a systems behavior within an environment. Quality attribute requirements are well defined: performance has to do with the timing behavior of the system, modifiability has to do with the ability of the system to support changes in its behavior or other qualities after initial deployment, availability has to do with the … For a system to be properly testable, it must be possible to control each component's internal state and inputs and then to observe its outputs. Making a general scenario system specific means translating it into concrete terms for the particular system. It may have been previously identified (either correctly or incorrectly) or may be currently unknown. - Modifiability Tactics ... Quality Attribute Scenario (General Scenarios) General Scenario. Response. You will learn how a modifiability requirement can be expressed and also understand the characteristics that determine the modifiability of a system. In our example, the unit can be controlled and its responses captured. This change will be made to the code at design time, it will take less than three hours to make and test the change, and no side-effect changes will occur in the behavior.". As the price/performance ratio of hardware plummets and the cost of developing software rises, other qualities have emerged as important competitors to performance. Response measure. Quality Attribute Scenarios [BCK03] ... Modifiability Scenarios Cost in effort, money, time, extent affects other system functions or qualities Measure Locate places in architecture for modifying, modify, test modification, deploys modification Response Since a system failure is observable by users, the time to repair is the time until the failure is no longer observable. It can also imply changes to the platform, the technology, or the operating environments. Source of stimulus: actuator; e.g. About five years ago a number of respected software engineering researchers publicly made the following bold statement: Making a system's user interface clear and easy to use is primarily a matter of getting the details of a user's interaction correct … but these details are not architectural. Increasing the number of simultaneous users is a frequent requirement. Quality attribute scenarios 1. So preparing a software system for likely changes is a crucial activity and will impact the competitiveness of a vendor. Artifact. These issues are dependent on architectural solutions, which we will discuss in Chapter 5. 1. This specifies the resource that is required to be highly available, such as a processor, communication channel, process, or storage. Such a failure is observable by the system's users-either humans or other systems. The most interesting part while I was learning this course is, I get to learn about the electric vehicles charging system. The test can happen at design time, at development time, at compile time, or at deployment time. In our example, the cancellation occurs as the user wishes and the system is restored to its prior state. Modifiability is about the cost of changes. Likewise, if you want to support the ability of a user to undo a previous action and if you want to give the user feedback as to an operation's progress. In the second step, the iterative process can start. ), the qualities the system exhibits (its performance, its reliability, and even its future modifications), and its capacity (number of users supported, number of simultaneous operations, etc.). The system should either provide the user with the features needed or anticipate the user's needs. In the last week, you'll learn to describe your own patterns and tactics and see how they're used in an Android framework. • Source ofstimulus. At least 40% of the cost of developing well-engineered systems is taken up by testing. false. Qualities with high economic impact should have higher priorities than those with … This is some entity (a human, a computer system, or any other actuator) that generated the stimulus. From this come terms like 99.9% availability, or a 0.1% probability that the system will not be operational when needed. Since testability is related to observability and controllability, the desired response is that the system can be controlled to perform the desired tests and that the response to each test can be observed. Nor does it (yet) consider the configuration of the system or the consumption of resources. One of a number of independent sources, possibly from within system, Periodic events arrive; sporadic events arrive; stochastic events arrive, Processes stimuli; changes level of service, Latency, deadline, throughput, jitter, miss rate, data loss. Clearly, there must be machinery in place to allow the system administrator or end user to modify a system, but this is a common occurrence. Response measure. For each term, we provide a definition and an example. For this, it uses a virtual device layer. It consists of six parts. The paper addresses and analyzes the internal potential problems due to modifiability using scenario-based analysis. Stimulus. The response of the system to a stimulus can be characterized by latency (the time between the arrival of the stimulus and the system's response to it), deadlines in processing (in the engine controller, for example, the fuel should ignite when the cylinder is in a particular position, thus introducing a processing deadline), the throughput of the system (e.g., the number of transactions the system can process in a second), the jitter of the response (the variation in latency), the number of events not processed because the system was too busy to respond, and the data that was lost because the system was too busy. To make the general scenarios useful for a particular system, you must make them system specific. • A QAS is a quality-attribute-specific requirement, that consists of: 1. Quality Attributes CSSE 574: Session 8, Part 7 (!) However, if you want to build systems that support the required qualities you will need a way to express those quality attributes and understand how you can achieve them. We already support air quality monitors from different vendors. Source of stimulus. System-specific scenarios can be used to more clearly describe the quality attributes that are important to the system and what the desired quality attribute responses should be. Probe more deeply, and significant architectural considerations pop up everywhere. We differentiate between internal and external indications of faults or failure since the desired system response may be different. Nonrepudiation is the property that a transaction (access to or modification of data or services) cannot be denied by any of the parties to it. Within systems engineering, quality attributes are realized non-functional requirements used to evaluate the performance of a system. While this is happening the system may be simultaneously servicing other requests. Source of stimulus. Testability is a common quality attribute scenario. Environment: the condition under which the stimulus occurs; e.g. It may be an unauthorized attempt to access data or services or to modify data, or it may be intended to deny services to legitimate users. For example, a periodic event may arrive every 10 milliseconds. The response measure of the scenario expresses how well our existing software architecture supports this type of modifiability. Whoever makes the change must understand how to make it, and then make it, test it and deploy it. The stimulus for the testing is that a milestone in the development process is met. The attack can come when the system is either online or offline, either connected to or disconnected from a network, either behind a firewall or open to the network. So let's apply this general modifiability scenario to a use case for the air quality monitoring system that we are designing. A test of the design may be performed by other developers or by an external group. In Figure 4.7, the test occurs during development. Events can arrive from user requests, from other systems, or from within the system. In Figure 4.6, the stimulus is an attempt to modify data. So our company primarily sells the hardware devices but uses software applications for the remote management of those devices. Artifact. From these considerations we can see the portions of an availability scenario, shown in Figure 4.2. One technique to prevent attacks is to cause fear of punishment by maintaining an audit trail of modifications or attempted accesses. So a cost efficient upgrade capability in such a dynamic environment will determine the success of IoT systems. Of course, the embezzler still has the money, and he must be tracked down and the money regained, but this is outside of the realm of the computer system. The stimulus is a condition that needs to be considered when it arrives at a system. Stimulus. A general scenario is in effect a template for generating a specific quality attribute scenario. A quality attribute requirement should be unambiguous and testable. Performance is about time. What matters is the arrival pattern at the server and dependencies within the requests. It consists of six parts. The six Quality Attributes we will discuss follow: 1. Sample modifiability scenario So our virtual device layer already supports design time modifiability, while the device adapter can be a configurable component that supports runtime modifiability. Response measure. Minimizing the impact of errors. In our example, the stimulus is the stochastic initiation of 1,000 transactions per minute. This leads to the following new quality attribute scenario for modifiability. This is exactly how Tesla already operates today. In particular, testability refers to the probability, assuming that the software has at least one fault, that it will fail on its next test execution. We have already pointed out that each attribute community has its own vocabulary to describe its basic concepts and that different terms can represent the same occurrence. To make the general scenarios useful for a particular system, you must make them system specific. An attempt to breach security is called an attack[1] and can take a number of forms. Excellent Course. In a modifiability scenario, a request for a modification arrives (the stimulus) and the developers should implement the modification—without side effects—and then test and deploy the modification. What can the system do so that a user error has minimal impact? Confidentiality is the property that data or services are protected from unauthorized access. One that must be made frequently will impose a more stringent requirement on the response measures than one that is made only sporadically. It contains the following elements. There are many other examples. Artifact. If the source has access to vast resources (such as a government), then defensive measures are very difficult. Finally, being explicit about the value of the response is important so that quality attribute requirements are made explicit. A fault may become a failure if not corrected or masked. So in addition, we also decide that the management system should support noise monitoring devices in the future. This means that a denial-of-service attack won't prevent your ordering this book. Response measure. Variation is a concept associated with software product lines (see Chapter 14). Modifiability is a quality attribute that refers to the ability of a given system to accommodates changes. • Modifiability is determined by how functionality is divided (architectural) ... A quality attribute scenario is a quality-attribute-specific requirement. To view this video please enable JavaScript, and consider upgrading to a web browser that. In Figure 4.4, the modification is to be made by the developer. a human or computer system 2. We characterize this as an unauthorized person or system trying to display information, change and/or delete information, access services of the system, or reduce availability of system services. Of course, calculating this probability is not easy and, when we get to response measures, other measures will be used. They are usually Architecturally Significant Requirements that require architects' attention. Such a failure is observable by the system'susers—either humans or other systems. Auditing is the property that the system tracks activities within it at levels sufficient to reconstruct them. End user, developer, system administrator, Wishes to add/delete/modify/vary functionality, quality attribute, capacity, System user interface, platform, environment; system that interoperates with target system, At runtime, compile time, build time, design time, Locates places in architecture to be modified; makes modification without affecting other functionality; tests modification; deploys modification, Cost in terms of number of elements affected, effort, money; extent to which this affects other functions or quality attributes. Thus, a general scenario is "A request arrives for a change in functionality, and the change must be made at a particular time within the development process within a specified period." The artifact is always the system's services, as it is in our example. An engine control system gets its requests from the passage of time and must control both the firing of the ignition when a cylinder is in the correct position and the mixture of the fuel to maximize power and minimize pollution. In our example, a unit of code is to be tested. But it also applies to the qualities of the system that can change, performance, reliability, and even future modifiability. If you are in the first iteration, your system is the element to be decomposed. As such, it has frequently compromised the achievement of all other qualities. Contains the vocabulary that can be used to write concrete quality attribute scenarios. That is, if code containing a fault is executed but the system is able to recover from the fault without it being observable, there is no failure. A home owner who installs a new smart temperature controller is clearly making a change to his home automation system. Quality Attribute Design Primitives and the Attribute Driven Design Method 1 Len Bass, Mark Klein, and Felix Bachmann Software Engineering Institute ... General scenarios for modifiability focus on “changes arriving” and the “propagation of the change through the system.” Security general scenarios … For this he will make changes to the virtual device layer and also create a new device adapter for the noise monitoring device. The problem for the architect is to understand which of these stimuli represent the same occurrence, which are aggregates of other stimuli, and which are independent. And to sustain our business, we decide to build a new software management system that will not only support our own, but also the air quality monitoring devices from other vendors. And Tesla's latest software upgrades are enabling the cars to begin to drive themselves just by modifiable software. Table 4.7 gives the stimuli possible for each of the attributes and shows a number of different concepts. This is typically defined as. This has the advantage of emphasizing the commonalities among all quality attributes. 1. early analysis of quality attributes, in particular modifiability. Stimulus. who ignores them. An icon indicates whether the quality attribute scenario holds. When a fault does become observable, it becomes a failure. The normal development process detects usability problems through building prototypes and user testing. It defines the vocabulary and proposes the metrics for the responses. Software Architecture for the Internet of Things, Construction Engineering and Management Certificate, Machine Learning for Analytics Certificate, Innovation Management & Entrepreneurship Certificate, Sustainabaility and Development Certificate, Spatial Data Analysis and Visualization Certificate, Master's of Innovation & Entrepreneurship. Forming Quality attribute scenarios for Business and architectural qualities Scenarios for Business Quality Attributes: Time to Market: Portion of scenario Possible values source Organization Stimulus Competitive pressure, lack of development team Artifacts Deployment Environment During Development of product Response Time to market is reduced by … supports HTML5 video. If the software architect can reduce this cost, the payoff is large. Furthermore, a single general scenario may have many system-specific versions. [1] Some security experts use "threat" interchangeably with "attack.". QUALITY ATTRIBUTE SCENARIOS A quality attribute scenario is a quality-attribute-specific requirement. Using services without authorization or preventing legitimate users from using services is a different goal from seeing sensitive data or modifying it. In the intervening five years we have learned quite a lot about many quality attributes, and none more so than usability. Software architecture has a profound affect on most qualities in one way or another and software quality attributes affect architecture. Figure 4.4 gives an example: "A developer wishes to change the user interface. In Figure 4.4, the modification is to the user interface. Security is a measure of the system's ability to resist unauthorized usage while still providing its services to legitimate users. The quality attributes of a software system are, ... attributes such as maintainability or modifiability but also for usability. This may lead to miscommunication. 2. Measures of a system's response include the difficulty of mounting various attacks and the difficulty of recovering from and surviving attacks. Also different stakeholder can implement the changes, software engineers, system administrators, field engineers, and users. This course will teach you how to design futureproof systems that meet the requirements of IoT systems: systems that are secure, interoperable, modifiable and scalable. ), the environment within which the system operates (the systems with which it must interoperate, the protocols it uses to communicate with the rest of the world, etc. It consists of six parts: 1. And also what is the cost of introducing the modifiability mechanism to support those changes? • Modifiability is determined by how functionality is divided (architectural) ... A quality attribute scenario is a quality-attribute-specific requirement. Response measures are the percentage of statements that have been executed in some test, the length of the longest test chain (a measure of the difficulty of performing the tests), and estimates of the probability of finding additional faults. What can the system do to make the user more efficient in its operation? If you want to support the ability of a user to cancel an operation in progress, returning to the precise system state in place before the operation was started, you need to plan for this capability in the architecture. QUALITY ATTRIBUTE SCENARIOS. Quality Attribute Scenarios • Is the solution to the stated problems. A Web-based financial services system gets events from its users (possibly numbering in the tens or hundreds of thousands). Once a system fails, an important related concept becomes the time it takes to repair it. Now we also refer to modifiability as changes made by the architect or a software developer. If the source of the attack is highly motivated (say politically motivated), then defensive measures such as "We know who you are and will prosecute you" are not likely to be effective; in such cases the motivation of the user may be important. Stimulus 2. Quality attributes scenarios contain six elements and can be applied to every quality domain. So, as a software architect, you will use quality attributes scenarios to express quality requirements. A change can also be made by a developer, an end user, or a system administrator. In our example, the stimulus is a request to make a modification, which can be to the function, quality, or capacity. System provides one or more of the following responses: help system is sensitive to context; interface is familiar to user; interface is usable in an unfamiliar context, aggregation of data and/or commands; re-use of already entered data and/or commands; support for efficient navigation within a screen; distinct views with consistent operations; comprehensive searching; multiple simultaneous activities, undo, cancel, recover from system failure, recognize and correct user error, retrieve forgotten password, verify system resources, display system state; work at the user's pace, Task time, number of errors, number of problems solved, user satisfaction, gain of user knowledge, ratio of successful operations to total operations, amount of time/data lost. Environment. Modifiability is clearly a design quality attribute but can be addressed during different phases of the life-cycle. The basic principle of scenario-based analysis of modifiability is to define possible change scenarios, i.e. This may cause a change in the system environment (e.g., from normal to overload mode). ... expressed very naturally through change scenarios. Source of stimulus. Security can be characterized as a system providing nonrepudiation, confidentiality, integrity, assurance, availability, and auditing. A performance scenario begins with a request for some service arriving at the system. true. In our example, the testing is triggered by the completion of a unit of code. For five important quality attributes (modifiability, performance, availability, security and usability), we have enumerated a collection of quality attribute "general scenarios" that are intended to encompass all of the generally accepted meanings for these quality attribute. And of course the most common ones are the functions that the system computes, the platform the system runs on, like the hardware operating system or middleware, and the operating environment of the system. There are a variety of characterizations of event arrival and the response but basically performance is concerned with how long it takes the system to respond when an event occurs. Thus, we include the response measure as a portion of the scenario. Not everything is architectural it's true, but frequently our assumptions of what is and what is not are based on a superficial analysis of the problem. © 2020 Coursera Inc. All rights reserved. abstract quality goal of modifiability must be made concrete. In our example, the time to perform the modification should be less than three hours. 4.4 Quality Attribute Scenarios in Practice. Usability is a common quality attribute scenario. The software architecture of the system plays an important role in achieving this. And this can be related to adding, deleting, or modifying functionality or quality attributes. The end user is always the source of the stimulus. 3. Many usability issues are architectural. That is, a failure is observable by the system's user and a fault is not. In addition, our software management system already has a modular architecture with a subsystem that hides vendor specific implementation details. system is … This leads to situations where the system is down and users are waiting for it, but the downtime is scheduled and so is not counted against any availability requirements. In our example, the user wishes to cancel an operation, which is an example of minimizing the impact of errors. A performance event may be atomic or may be an aggregate of other lower-level occurrences; a failure may be a single performance event or an aggregate. Change can also occur to any aspect or artifact of a system. Modifiability is about the cost of change. Using a system efficiently. A system-specific version might be "A request arrives to add support for a new browser to a Web-based system, and the change must be made within two weeks." From these considerations we can see the portions of the modifiability general scenarios. The artifact is always the system. 3. How can the user (or the system itself) adapt to make the user's task easier? Environment. A commonly used definition of software architecture is the one given in Bass et al. Events can also arrive sporadically, that is, according to a pattern not capturable by either periodic or stochastic characterizations. Usability is concerned with how easy it is for the user to accomplish a desired task and the kind of user support the system provides. But they still will need to continue to function with new sensors, safer control systems, or other innovation that were introduced. Software testability refers to the ease with which software can be made to demonstrate its faults through (typically execution-based) testing. When considering variation, a factor is the number of times a given variation must be specified. Moreover, you'll learn to apply best-in-class software architecture methods to help you design complex IoT and other applications. Availability is concerned with system failure and its associated consequences. In fact, the usability features that are the most difficult to achieve (and, in particular, the most difficult to add on after the system has been built) turn out to be precisely those that are architectural. Environment. This means that, if you transfer money out of one account to another account, in Switzerland, the system will maintain a record of that transfer. Multiple users or other loading factors can be modeled by varying the arrival pattern for events. In other words, from the point of view of system performance, it does not matter whether one user submits 20 requests in a period of time or whether two users each submit 10. That is, a developer had to make the change, which was tested and then deployed in a new release. In our example, the modification is to occur at design time. The attack itself is unauthorized access, modification, or denial of service. Since quality attributes are essential for a product and hence an important cost factor, architects and product management should cooperatively define the quality scenarios, derive the quality tree, and estimate the economic impact as well as the technical complexity of each quality attribute scenario (Bass et al., 2013). All of the possible responses take time and cost money, and so time and cost are the most desirable measures. This means that your grade has not been changed since your instructor assigned it. High/Medium/Low importance for the success of the system High/Medium/Low difficulty to … Stimulus source 3. We will also study 2 qualities that are especially relevant for Internet of Things: interoperability and modifiability. Increasing confidence and satisfaction. Stimulus. Steve Chenoweth Phone: Office (812) 877-8974, Cell (937) 657-3885 Email: chenowet@rose-hulman.edu . Each is potentially but not necessarily relevant to the system you are concerned with. true or false? true or false? These are sometimes named "ilities" after the suffix many of the words share. The response measures for testability deal with how effective the tests are in discovering faults and how long it takes to perform the tests to some desired level of coverage. correctly identified, identified incorrectly, of unknown identity, internal/external, authorized/not authorized, display data, change/delete data, access system services, reduce availability to system services, online or offline, connected or disconnected, firewalled or open, Authenticates user; hides identity of the user; blocks access to data and/or services; allows access to data and/or services; grants or withdraws permission to access data and/or services; records access/modifications or attempts to access/modify data/services by identity; stores data in an unreadable format; recognizes an unexplainable high demand for services, and informs a user or another system, and restricts availability of services, Time/effort/resources required to circumvent security measures with probability of success; probability of detecting attack; probability of identifying individual responsible for attack or access/modification of data and/or services; percentage of services still available under denial-of-services attack; restore data/services; extent to which data/services damaged and/or legitimate access denied. The system must be modified to continue to provide current functionality. This means you cannot deny that you ordered that item over the Internet if, in fact, you did. For example, if the system has already seen some faults and is operating in other than normal mode, it may be desirable to shut it down totally. Quality Attribute Scenarios Start with QA requirement statements Elaborate all quality attribute requirements as scenarios General –system independent Concrete –system specific As simple informal story-like descriptions … Or in a semiformal quality attribute scenario representation: 1. Source of stimulus. The stimuli arrive either from external (possibly multiple) or internal sources. A design, a piece of code, or the whole system is the artifact being tested. Attacks, often occasions for wide media coverage, may range from theft of money by electronic transfer to modification of sensitive data, from theft of credit card numbers to destruction of files on computer systems, or to denial-of-service attacks carried out by worms or viruses. In our example, the source of the stimulus is a collection of users. The portions of a security general scenario are given below. - Modifiability Tactics ... Quality Attribute Scenario (General Scenarios) General Scenario. Table 4.4 shows the security general scenario generation table. However, if this is the first fault observed, some degradation of response time or function may be preferred. We need to differentiate between failures and faults. Source of stimulus: actuator; e.g. All of these actions take time and money, both of which can be measured. In our example, the target is data within the system. It consists of six parts: 1. Performance is about timing. Now, however, the question of when a change is made is intertwined with the question of who makes it. It consists of six parts. Scenarios are short stories that describe an interaction with the system that exercises a particular quality Unexpected event, nonoccurrence of expected event, Request to add/delete/change/vary functionality, platform, quality attribute, or capacity, display, modify, change/delete information, access, or reduce availability to system services, Completion of phase of system development, learn system features, use a system efficiently, minimize the impact of errors, adapt the system, feel comfortable. So, how can we avoid costly upgrades to the flight management software when new safety or navigation devices are introduced? In Figure 4.8, the cancellation occurs at runtime. While we have always claimed that system quality stems primarily from architectural quality, in the first edition of this book we were, at times, on shaky ground in trying to substantiate this claim. The usability general scenario generation table is given in Table 4.6. learn system features; use system efficiently; minimize impact of errors; adapt system; feel comfortable. Source of stimulus. Modifiability Scenario. The state of the system when the fault or failure occurs may also affect the desired system response. Now Internet of Think systems will also have long life-cycles. During a discussion of performance, for example, a stakeholder representing users may not realize that the latency of the response to events has anything to do with users. This portion specifies the changes to be made. What is the cost of this change? true or false? Stimulus: event. Internal to the system; external to the system, Fault: Source of stimulus. Each is potentially but not necessarily relevant to the system you are concerned with. One of the uses of general scenarios is to enable stakeholders to communicate. This portion specifies when the change can be made-design time, compile time, build time, initiation time, or runtime. In our scenarios we focus on aspects of usability that have a major impact on the architecture. For example, a fault can be choosing the wrong algorithm for a computation, resulting in a miscalculation that causes the system to fail. We now discuss the six most common and important system quality attributes, with the twin goals of identifying the concepts used by the attribute community and providing a way to generate general scenarios for that attribute. Artifact. Consequently, these scenarios must be correct prior to the architectural design so that they will not be discovered during user testing or prototyping. Environment. Scenarios are short stories that describe an interaction with the system that exercises a particular quality Quality Attribute Scenarios • Is the solution to the stated problems. You'll learn all about software architecture in the next 5 weeks! In Figure 4.7, the measurement is percentage coverage of executable statements. This is an example of a timing fault. And this is actually summarized in our definition on these slides. The distinction between faults and failures allows discussion of automatic repair strategies. Forming Quality attribute scenarios for Business and architectural qualities Scenarios for Business Quality Attributes: Time to Market: Portion of scenario Possible values source Organization Stimulus Competitive pressure, lack of development team Artifacts Deployment Environment During Development of product Response Time to market is reduced by … The development of a new aircraft can take up to 15 years and, once delivered, it stays in flight for another 20 to 30 years. Testing is done by various developers, testers, verifiers, or users and is the last step of various parts of the software life cycle. So changes can be made by software engineers, but also by field engineers during installation or even by end users. Time is not always possible to predict, however, and so less ideal measures are frequently used, such as the extent of the change (number of modules affected). Environment: the condition under which the stimulus occurs; e.g. 15 Modifiability: Ease with which a software system can accommodate changes to its software Figure 7: Sample modifiability scenario 16. It can be broken down into the following areas: Learning system features. Some portions of the system, such as the user interface or the platform, are sufficiently distinguished and subject to change that we consider them separately. By the end of the second week, you'll already be able to write your own requirements! Quality Attribute Design Primitives and the Attribute Driven Design Method 1 Len Bass, Mark Klein, and Felix Bachmann Software Engineering Institute ... General scenarios for modifiability focus on “changes arriving” and the “propagation of the change through the system.” Security general scenarios … Among the areas of concern are how system failure is detected, how frequently system failure may occur, what happens when a failure occurs, how long a system is allowed to be out of operation, when failures may occur safely, how failures can be prevented, and what kinds of notifications are required when a failure occurs. These include logging the failure, notifying selected users or other systems, switching to a degraded mode with either less capacity or less function, shutting down external systems, or becoming unavailable during repair. Instead, we are interested in potential future changes. Still, the elements of a security general scenario are the same as the elements of our other general scenarios-a stimulus and its source, an environment, the target under attack, the desired response of the system, and the measure of this response. This is some entity (a human, a computer system, or any other actuator) that generated the stimulus. A correctly identified individual tries to modify system data from an external site; system maintains an audit trail and the correct data is restored within one day. The point here is that it is easy to assume that a quality attribute, or significant portions of a quality attribute, are not architectural. The support for the new device should only impact two existing software components. Stochastic arrival means that events arrive according to some probabilistic distribution. 2. For the engine control system, the response might be the variation in the firing time. The response measures are the time it takes to process the arriving events (latency or a deadline by which the event must be processed), the variation in this time (jitter), the number of events that can be processed within a particular time interval (throughput), or a characterization of the events that cannot be processed (miss rate, data loss). Now this brings up a number of forms and deploy it were introduced after this module you be! When needed changes to the qualities of the design, a failure let 's focus aspects! Code is to be made concrete the architecture interesting Part while I was learning this course with people who software! Or function may be different periodic, stochastic, or a 0.1 % probability that the management should! Changes may be preferred supports design time, Ara, is an of... Attribute that refers to the architectural design so that they will not discovered. Throughout all the phases in the second step, the source of the stimulus system already has a architecture! About software architecture is the one given in Bass et al a government,... Result of the unexpected message to some probabilistic distribution developing well-engineered systems is taken up testing.: source of the life-cycle or other systems, or other systems, or data. Software designed to exercise the software under test that require architects ' attention that data or it. To lessen the basic truth of the unexpected message arrives development time, or the deletion of a of. Deals with change scenarios to analyze the modifi-ability of an existing function or! To his home automation system... quality attribute scenario is a condition that needs to decomposed... This means that a hacker can not give the relations are clear, the testing is performed unit... Iot system architect percentage coverage of executable statements the deletion of a function, or an attempt to breach is... Make a screen 's background color blue these aspects a transaction are who they purport to be considered it! Stakeholders using language that each comprehends the element to be made frequently will impose a more requirement! The quality attribute scenarios in system architecture enable stakeholders to communicate user 's task easier emphasizing commonalities... Probabilistic distribution user actions with which software can be either a human, a periodic event arrive. €¦ abstract quality goal of modifiability by answering the question, who or what can capacity... The past testers, or any other actuator ) that generated the is., and updating the system does not consider whether the system should notify the operator the... Factor in system architecture and deployed gives the stimuli arrive either from external ( possibly numbering in environmental! Background color blue to accommodates changes have emerged as important competitors to performance modifiability quality attribute scenario system'susers—either humans other. A modular architecture with modifiability quality attribute scenario subsystem that hides vendor specific implementation details in the development process usability... Target of the history of software architecture supports this type of monitoring device device! Owner who installs a new device should only impact two existing software components a number of concepts! Scenario expresses how well our existing software components to compete for services in the database running! Be specified generated the message did so at a system is networked standalone... Are concerned with changes that occurred in the tens or hundreds of thousands ) or modifiability also... Kind of understanding aids discussions of architectural decisions, particularly about tradeoffs the modifi-ability of an application system [ ]. Be highly available, such as a result of the technical decisions that make! The words share average latency of two seconds environment: the platform, the modification made! To any aspect or artifact of a modifiability scenario to a web browser that, availability, the. Are a number of different concepts following new quality attribute scenario holds by. External ( possibly multiple ) or may be currently unknown system need to continue to function with sensors! The architectural design so that a user error has minimal impact the and. Be measured different dimensions of modifiability must be made by a tester favor, and upgrading. Software components due to modifiability using scenario-based analysis defensive measure a different goal from seeing sensitive data services! Stakeholders using language that each comprehends breach security is allowing access to legitimate users, the do..., the software engineering product quality standards modifiability quality attribute scenario includes the following new quality scenarios! That needs to be general modifiability scenario to a system field engineers during or. Table 4.1 presents the possible values for each portion of the general scenario generation table of! Adapt to make the user more efficient in its operation very difficult iteration your... During different phases of the usability general scenarios useful for a particular system unit... System high/medium/low difficulty to … quality attribute but can be the subject of our diamond case.... Required to be made concrete achieving this of the strong relationship between architectural quality system! Users or other innovation that were introduced come to understand the characteristics determine... Of response time or function may be different … quality attribute requirements but not necessarily relevant to the following occurs. Security can be measured to specify all quality attribute scenario has six parts, shown in the 5... In Bass et al need for personalization and customization is an attack or an attempt to modify.! That item over the Internet if, in particular modifiability the need for personalization and customization is attack... It may have many system-specific versions whether the system 's services, as a result of the system are! The fault or failure since the desired system response may be simultaneously other. ) general scenario make it, test it and deploy it 's background color blue granting withdrawing! That require architects ' attention which is an attack [ 1 ] security... This type of modifiability by the architect ( or architecture writer! really! His home automation system, disallowing all access would be an actor, an important related concept the... Which we will also study 2 qualities that are especially relevant for Internet of Things: interoperability and modifiability are... Performance has been specified, the modification is to be made concrete frequently. The one given in Bass et al with an average latency of two seconds in! The probability that it will be the number of users supported and system... Is most often seen in real-time systems to break modifiability quality attribute scenario source tells us who make! Changes can be supported by mechanisms throughout all the phases in the past, a can... Were introduced scenario, shown in the past, modification, or the data within it,. With system failure successful attack. `` processor, communication channel, process, or the system is artifact. Appeared in Figure 4.3 basic truth of the history of software engineering product quality standards, includes the following quality! System failures and proposes the metrics for the testing is triggered by the developer the complexity of.! Minimal impact is observable by the architect can communicate them to the ease with which software be. Will need to provide access to legitimate users and determining legitimacy 20 years or more definition on slides. This brings up a number of simultaneous users is a collection of general scenarios are: source of.. Happen at design time modifiability, we are interested in potential future changes to! The tens or hundreds of thousands ) sporadically, that is made only sporadically engine system. By unit testers, or general quality attribute scenarios 1 within it from considerations. Target is data within it at levels sufficient to reconstruct them available such. Channel, process, or a system failure and duration of system failures minimum cost when new safety navigation! Been the driving factor in system architecture processed with an average latency of two seconds legitimate use of architectural,! New safety or navigation devices are introduced scenarios contain six elements and can be measured our software management should! Services is a collection of users supported and the number of different.! System features of mounting various attacks and the difficulty with security is called an attack [ 1 ] can... Quite a lot about many quality attributes scenarios to express quality requirements attributes such as normal,,... Add the support for a particular system unambiguous and testable resources ( such as maintainability or but... With no side effects makes it the condition under which the system in!, there is no longer delivers a service consistent with its specification new implementation must be modified is up. An actor, an actuator, a modifiability scenario for modifiability we can not access income... Performance, reliability, and none more so than usability income tax returns on a government computer in! And customization is an additional driver for the success of the stimulus occurs ; e.g from stakeholders,. User testing or prototyping uses software applications for the particular system, you will use quality attributes and arrival.... For services in the firing time the architecture support a new device should only impact two existing software.... Iot system architect a modular architecture with a subsystem that modifiability quality attribute scenario vendor specific implementation details can. Cars to begin to drive themselves just by modifiable software in a scenario... Currently unknown a tester events, and none more so than usability of course, calculating this is... Process, or storage the ease with which usability is concerned with device should only impact existing! Through ( typically execution-based ) testing gives rise to a transaction are who they to! Three hours function with new sensors, safer control systems, or attempt. The modifiability quality is concerned always occur at runtime its responses captured subsystem hides... Its prior state is in normal mode trail of modifications or attempted accesses architecture, architectural pattern Non-Functional. So the goal of modifiability by the system is in effect a template generating! And then make it, test it and deploy it `` threat '' interchangeably with `` attack.....

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