modifiability quality attribute scenario

Multiple users or other loading factors can be modeled by varying the arrival pattern for events. Satisfying the request requires resources to be consumed. 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. In Figure 4.4, the modification is to be made by the developer. Environment. Now it's the need for personalization and customization is an additional driver for the support of modifiability by the end user. To view this video please enable JavaScript, and consider upgrading to a web browser that. Finally, being explicit about the value of the response is important so that quality attribute requirements are made explicit. This has the advantage of emphasizing the commonalities among all quality attributes. 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. Stimulus. After this module you should be able to formulate your own quality requirements. In our example, the stimulus is a request to make a modification, which can be to the function, quality, or capacity. 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 … 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. When is the change made and who makes it (the environment). In the example, the scenario is violated since the change cannot … However, if this is the first fault observed, some degradation of response time or function may be preferred. A sample modifiability scenario is "A developer wishes to change the user interface to make a screen's background color blue. This is some entity (a human, a computer system, or any other actuator) that generated the stimulus. 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 … Figure 4.8 gives an example of a usability scenario: A user, wanting to minimize the impact of an error, wishes to cancel a system operation at runtime; cancellation takes place in less than one second. Source of stimulus. true. You will learn how a modifiability requirement can be expressed and also understand the characteristics that determine the modifiability of a system. 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. sequences of events, and assess their impact on the system. 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. Testing is done by various developers, testers, verifiers, or users and is the last step of various parts of the software life cycle. It contains the following elements. Artifact. A home owner who installs a new smart temperature controller is clearly making a change to his home automation system. Now Internet of Think systems will also have long life-cycles. QUALITY ATTRIBUTE SCENARIOS A quality attribute scenario is a quality-attribute-specific requirement. 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. High/Medium/Low importance for the success of the system High/Medium/Low difficulty to … Stimulus. Stimulus. In our example, the target is data within the system. The point here is that it is easy to assume that a quality attribute, or significant portions of a quality attribute, are not architectural. 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. Source of stimulus. 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. 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." 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. Availability is concerned with system failure and duration of system failures. 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. In the last five years, our understanding of the relation between usability and software architecture has deepened (see the sidebar Usability Mea Culpa). An audit trail is also useful in correcting from a successful attack. 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. Source of stimulus. 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." And this can be related to adding, deleting, or modifying functionality or quality attributes. system is … In Figure 4.6, the stimulus is an attempt to modify data. 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 Stimulus. These issues are dependent on architectural solutions, which we will discuss in Chapter 5. 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? 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. To view this video please enable JavaScript, and consider upgrading to a web browser that true or false? 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. This is some entity (a human, a computer system, or any other actuator) that generated the stimulus. By the end of the second week, you'll already be able to write your own requirements! Facilitating this kind of understanding aids discussions of architectural decisions, particularly about tradeoffs. Response. In our example, the unexpected message arrives from outside the system. That is, a failure is observable by the system's user and a fault is not. So our company primarily sells the hardware devices but uses software applications for the remote management of those devices. It consists of six parts: 1. The system must be modified to continue to provide current functionality. 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.). And now we want to add the support for noise monitoring. The artifact is always the system. Not only does the system need to provide access to legitimate users, but it needs to support the granting or withdrawing of access. In Figure 4.4, the modification is to the user interface. From these considerations we can see the portions of the modifiability general scenarios. Auditing is the property that the system tracks activities within it at levels sufficient to reconstruct them. Response. One, maintainability is the capability of the software to be modified. General scenarios provide a framework for generating a large number of generic, system-independent, quality-attribute-specific scenarios. The basic principle of scenario-based analysis of modifiability is to define possible change scenarios, i.e. The most interesting part while I was learning this course is, I get to learn about the electric vehicles charging system. In Figure 4.8, the cancellation should occur in less than one second. 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. true or false? Sample modifiability scenario This is typically defined as. 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. Each of these security categories gives rise to a collection of general scenarios. The quality attributes provide the means for measuring the fitness and suitability of a product. 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. Such a failure is observable by the system'susers—either humans or other systems. This is some entity (a human, a computer system, or any other actuator) that generated the stimulus. For each term, we provide a definition and an example. The testing is performed by unit testers, integration testers, system testers, or the client. The response measure of the scenario expresses how well our existing software architecture supports this type of modifiability. The end user is always the source of the stimulus. The six Quality Attributes we will discuss follow: 1. Usability is a common quality attribute scenario. 15 Modifiability: Ease with which a software system can accommodate changes to its software Figure 7: Sample modifiability scenario 16. In our example, the transactions should be processed with an average latency of two seconds. Artifact. The component that generated the message did so at a different time than expected. They are usually Architecturally Significant Requirements that require architects' attention. Qualities with high economic impact should have higher priorities than those with … So, as a software architect, you will use quality attributes scenarios to express quality requirements. Using a system efficiently. I highly recommend this course with people who are software architects and who intended to become one day. And also what is the cost of introducing the modifiability mechanism to support those changes? 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. 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. Software Architecture, Architectural Pattern, Non-Functional Requirement, Software Requirements. We use a common form to specify all quality attribute requirements. Modifications may include corrections, improvements, or adaptations to changes in the environment or even the functional requirements. Lastly, you'll come to understand the business impact of the technical decisions that you make as an IoT system architect. In Figure 4.7, the test occurs during development. For the Web-based financial system, the response might be the number of transactions that can be processed in a minute. The system must process the arriving events. Now this brings us to the general scenario for modifiability. Nor does it (yet) consider the configuration of the system or the consumption of resources. Source of stimulus: actuator; e.g. An attempt to breach security is called an attack[1] and can take a number of forms. It consists of six parts. - Modifiability Tactics ... Quality Attribute Scenario (General Scenarios) General Scenario. 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. While this is happening the system may be simultaneously servicing other requests. This is an example of a timing fault. 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. Modifiability is clearly a design quality attribute but can be addressed during different phases of the life-cycle. abstract quality goal of modifiability must be made concrete. Quality Attributes CSSE 574: Session 8, Part 7 (!) Reveals the driving quality attribute requirements of a software- intensive system • scenario based . 1. 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). 3. The source of the attack may be either a human or another system. The stimulus is a condition that needs to be considered when it arrives at a system. 1. What is the cost of this change? Stimulus. One of the things that make performance complicated is the number of event sources and arrival patterns. A general scenario is in effect a template for generating a specific quality attribute scenario. And woe to the architect (or architecture writer!) As such, it has frequently compromised the achievement of all other qualities. 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. It can also imply changes to the platform, the technology, or the operating environments. And this will really allow us to compete for services in the environmental monitoring area. The stimulus for the testing is that a milestone in the development process is met. Source of stimulus. The quality attributes of a software system are, ... attributes such as maintainability or modifiability but also for usability. It defines the vocabulary and proposes the metrics for the responses. Variation is a concept associated with software product lines (see Chapter 14). supports HTML5 video. We differentiate between internal and external indications of faults or failure since the desired system response may be different. The stimuli are the event arrivals. We need to differentiate between failures and faults. In our example, the modification is made with no side effects. 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. 2. One technique to prevent attacks is to cause fear of punishment by maintaining an audit trail of modifications or attempted accesses. 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. Scheduled downtimes (i.e., out of service) are not usually considered when calculating availability, since the system is "not needed" by definition. And the total effort for implementing it should be less than 20 days. Figure 4.6 presents an example. This specifies the resource that is required to be highly available, such as a processor, communication channel, process, or storage. The paper addresses and analyzes the internal potential problems due to modifiability using scenario-based analysis. In our example, the unit can be controlled and its responses captured. Using services without authorization or preventing legitimate users from using services is a different goal from seeing sensitive data or modifying it. Each is potentially but not necessarily relevant to the system you are concerned with. 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. We will also study 2 qualities that are especially relevant for Internet of Things: interoperability and modifiability. Source of stimulus. In Figure 4.3, there is no downtime as a result of the unexpected message. 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. Change can also occur to any aspect or artifact of a system. One that must be made frequently will impose a more stringent requirement on the response measures than one that is made only sporadically. Availability is concerned with system failure and its associated consequences. The modifiability quality is concerned with what can change, when are changes made, and who makes the changes. And it supports a broad range of air quality monitoring devices. For this he will make changes to the virtual device layer and also create a new device adapter for the noise monitoring device. Those changes may be to add, delete, or modify any one of these aspects. In our scenarios we focus on aspects of usability that have a major impact on the architecture. All of these actions take time and money, both of which can be measured. a human or computer system 2. Many usability issues are architectural. This includes evolving, changing, and updating the system. So preparing a software system for likely changes is a crucial activity and will impact the competitiveness of a vendor. 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. It consists of six parts: 1. 4.4 Quality Attribute Scenarios in Practice. Performance is about timing. We cannot give the relations among stimuli in a general way because they depend partially on environment. ), 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. Environment. 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. Response. One such technique is quality-attribute-scenario analysis, which captures architecturally focused requirements from stakeholders. Source of stimulus: actuator; e.g. Events can also arrive sporadically, that is, according to a pattern not capturable by either periodic or stochastic characterizations. 3. Once a system fails, an important related concept becomes the time it takes to repair it. 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. Confidentiality is the property that data or services are protected from unauthorized access. In addition, our software management system already has a modular architecture with a subsystem that hides vendor specific implementation details. We also realize that many new vendors are entering these markets. Source of stimulus. So a cost efficient upgrade capability in such a dynamic environment will determine the success of IoT systems. Quality attribute scenarios 1. 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. Scenarios are short stories that describe an interaction with the system that exercises a particular quality The portions of a security general scenario are given below. 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). 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. In Figure 4.8, the cancellation occurs at runtime. In Figure 4.7, the measurement is percentage coverage of executable statements. 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. The software architecture of the system plays an important role in achieving this. • Source ofstimulus. However, in many situations, other people involved in a software system can also make modifications. This is some entity (a human, a computer system, or any Modifiability is a common quality attribute scenario. Changes used to be made to source code by a developer and were deployed in the next release. The attack itself is unauthorized access, modification, or denial of service. An arrival pattern for events may be characterized as either periodic or stochastic. An icon indicates whether the quality attribute scenario holds. omission, crash, timing, response, System's processors, communication channels, persistent storage, processes, degraded mode (i.e., fewer features, a fall back solution). 3. 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. And Tesla's latest software upgrades are enabling the cars to begin to drive themselves just by modifiable software. Internal to the system; external to the system, Fault: And it can change capacity, like the number of users supported and the number of simultaneous operations. In our example, the audit trail allows the accounts from which money was embezzled to be restored to their original state. This means that your grade has not been changed since your instructor assigned it. This leads to the following new quality attribute scenario for modifiability. Environment. 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 may be as simple as a playback capability for data recorded across various interfaces or as complicated as a testing chamber for an engine. Response measure. Environment. who ignores them. This may cause a change in the system environment (e.g., from normal to overload mode). 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. Modifiability is a quality attribute that refers to the ability of a given system to accommodates changes. In our example, the modification is to occur at design time. Quality attribute scenarios 1. (typically performance, modifiability, security, and availability) Scenarios are the leaves Output: a characterization and prioritization of specific quality attribute requirements. 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. Response. Smart transportation systems or intelligent energy management could remain operational for 20 years or more. Stimulus: event. Table 4.4 shows the security general scenario generation table. 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. Modifiability is about the cost of changes. So, how can we avoid costly upgrades to the flight management software when new safety or navigation devices are introduced? But they still will need to continue to function with new sensors, safer control systems, or other innovation that were introduced. 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. If the source has access to vast resources (such as a government), then defensive measures are very difficult. The domain specific, or general quality attribute scenario. In the third and fourth week, you will learn how to correctly write quality attributes and quality attribute scenarios for a specific case. A Web-based financial services system gets events from its users (possibly numbering in the tens or hundreds of thousands). 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. 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. 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. Quality attributes scenarios contain six elements and can be applied to every quality domain. Modifiability is about the cost of change. 2. system is … So changes can be made by software engineers, but also by field engineers during installation or even by end users. It also displays an estimate for the modifiability of the current scenario, that is, the number of man-days needed to implement the scenario. A design, a piece of code, or the whole system is the artifact being tested. 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. Modifiability is a quality attribute that refers to the ability of a given system to accommodates changes. A commonly used definition of software architecture is the one given in Bass et al. Modifiability is about the cost of change, both in time and money. A fault of one of the following classes occurs. For this, it uses a virtual device layer. Integrity is the property that data or services are being delivered as intended. 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. The system should either provide the user with the features needed or anticipate the user's needs. ... expressed very naturally through change scenarios. There are a number of possible reactions to a system failure. Consequently, these scenarios must be correct prior to the architectural design so that they will not be discovered during user testing or prototyping. For example, a fault can be choosing the wrong algorithm for a computation, resulting in a miscalculation that causes the system to fail. Stimulus. This portion specifies who makes the changes-the developer, a system administrator, or an end user. 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. Scenarios are short stories that describe an interaction with the system that exercises a particular quality 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 …

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