[Kumar 10b] Kiran Kumar and T. V. Prabhakar. Along the way, the evaluation team documents the relevant architectural decisions and identi es and catalogs their risks, non-risks, and tradeo s. For wellknown approaches, the evaluation team asks how the architect overcame known weaknesses in the approach or how the architect gained assurance that the approach su ced. Figure 13.1 Sample usability scenario 13.2 Tactics for Usability Figure 13.2 shows the goal of the set of usability tactics. But it was okay. To exercise this point, think about the design of the systems of roads and highways where you live. [Pang 16] C. Pang, A. Hindle, B. Adams, and A. Hassan. To gain an overview of the architectural choices made to support modi ability, the analyst asks each question and records the answers in the table. Can you think of any that should be added? Also, dont think of documentation as a step that is distinct from and follows design. 20.7 Summary Design is hard. These stakeholders will likely want to see the following artifacts: Interface documentations for those elements with which their system will interact, as found in module and/or C&C views The data model for the system with which their system will interact Top-level context diagrams from various views showing the interactions Maintainers use architecture as a starting point for maintenance activities, revealing the areas a prospective change will a ect. Quantum computers hold promise to speed up matrix inversion in this context. Responsibilities. Software validation and testing is a terri cally expensive task, undertaken with very nite budgets. Detect service denial. T User authentication is the basis for most types of access control and for user accountability. The output of an architecture evaluation includes an identi cation of risky portions of the architecture. Moreover, if the new deployment is not meeting its speci cations, it may be rolled back, again within a predictable and acceptable amount of time and e ort. In that case, even if you have found a framework that could be useful for your needs, you may need to discard it if it does not carry an approved license. All can be designed, evaluated, and documented; all answer to requirements; all are intended to satisfy stakeholders; all consist of structures, which in turn consist of elements and relationships; all have a repertoire of patterns at their respective architects disposal; and the list goes on. Finally, sensitive data is frequently separated from nonsensitive data to reduce the possibility of attack by users who have access to nonsensitive data. That guiding hand belongs to an architect, regardless of their title. Such transitions should be seamless to the user. Also recognize that di erent people need to know di erent kinds of information about the interface. Multiple case studies of applying the ATAM are available. Usability ROI Declining, But Still Strong, useit.com/alertbox/roi.html. Put another way, you choose what information is permissible and appropriate for people to assume about the element. Is there a di erent de nition of software architecture that you are familiar with? Until an organization has established a working method for coordinating among distributed teams, misunderstandings among the teams will likely cause delays and, in some cases, serious defects in a project. INCOSE is trying to move the engineering eld from a documentbased mentality to a model-based mentality, where structural models, behavioral models, performance models, and more are all used consistently to build systems better, faster, and cheaper. Unlike the evaluation team and the project decision makers, stakeholders do not participate in the entire exercise. The load balancer implements some form of the schedule resources tactic. This process results in one of the most basic of architectural structuresmodule decomposition. Discuss the strengths and weaknesses of doing this kind of architecture analysis as compared with the methods discussed in Chapter 21. Again, this distance may be seen as related to behavioral distance, but it should be consciously analyzed. 7. Be Mentored While experience may be the best teacher, most of us will not have the luxury, in a single lifetime, to gain rsthand all the experience needed to make us great architects. As a consequence, the load balancer has no information about whether a message was processed by a service instance, or how long it took to process a message. These design decisions can have a signi cant impact with respect to achieving QAs such as performance. This is done to reduce the container load timeyour service is constrained to be a thin image layer on top of the providers base image layer. 2. A VM is booted just as a bare-metal physical machine is booted. Condition monitoring provides the input to a predictive model and to sanity checking. The cloud service provider features that support this capability are called function-as-a-service (FaaS). Document the interface to a light bulb. What is the point of this discussion? Publish-Subscribe Pattern Publish-subscribe is an architectural pattern in which components communicate primarily through asynchronous messages, sometimes referred to as events or topics. The publishers have no knowledge of the subscribers, and subscribers are only aware of message types. 8. A relationship may dictate that one customer can have one or more accounts, and one account is associated with one or more customers. Those scenarios may already exist (perhaps as a result of a prior requirements-capture exercise or ADD activity), but if not, they are generated by the participants as part of the ATAM exercise. The VM image must be loaded and connected to the network, and the operating system must boot before it will be ready to process messages. But performance remains of fundamental importance. That is, a developer had to make the change, which was tested and then deployed in a new release. A high-priority event stream can be dispatchedassigned to a resource only if that resource is available. Tradeo s: Dependency injection makes runtime performance less predictable, because it might change the behavior being tested. The Soviet system had mistaken a rare sunlight condition for missiles in ight. Security often imposes procedures and processes that seem like needless overhead to the casual user. How would you respond? This le is speci c to the tool you are using to create the container image. Drumnadrochit Education, 2010. The behavior of elements embodies how they interact with each other and with the environment. The cooperating elements must agree on behavior, particularly with respect to the states and modes of the system. Table 24.1 identi es the knowledge area described by the PMBOK and the software architects role in that area. Of course, the humans dont always get it right when the computers get it wrong. ASRs can be extracted from a requirements document, captured from stakeholders during a workshop (e.g., a QAW), captured from the architect in a utility tree, or derived from business goals. In addition, documentation is especially important in distributed development. Minimum Security Requirements for Federal Information and Information Systems, FIPS Pub. Availability is also closely related to performance, since it may be di cult to tell when a system has failed and when it is simply being egregiously slow to respond. Testers and integrators deserve special attention because it is not unusual for a project to spend roughly half of its overall e ort in testing. But there is a sel sh reason to mentor as well: We nd that teaching a concept is the litmus test of whether we deeply understand that concept. Chapter 18 - Security Auditing Most widely used commercially available modeling tools employ notations in this category. For example, a publish-subscribe connector might have an arbitrary number of publishers and subscribers. Sensor fusion. In systems employing TMR, the statistical likelihood of two or more components failing is vanishingly small, and three components represents a sweet spot between availability and cost. This process gives the architect both the knowledge and the tools to identify and manage such debt. Another responsibility with caching is choosing the data to be cached. These scheduled allocations should be based on historical data about the pattern of usage of your services. 3. Second, service instance 1 may fail after it has acquired the lock, preventing service instance 2 from proceeding. Suppose the same element will now be used in a high-security system. This kind of deterioration is a form of technical debt, called architecture debt. We expect architectural views, as introduced in Chapter 1 and described in detail in Chapter 22, to be the primary vehicle by which the architect conveys the architecture. I put a test in the code so that the next time the race condition occurred, a debugging process was triggered. Study after study shows that most of the cost of the typical software system occurs after it has been initially released. A battery manager is responsible for periodically querying that component to retrieve the state of the battery. This kind of coordination is easy if it involves a short conversation at the shared vending machines, but its not so easy if it involves a preplanned web conference at a time when it is the middle of the night for one of the teams. Our opening quotation gives one example of the importance of these decisions. The need for education in computer security and related topics. 2 (AprilJune 2010): 145160. Working with Other Quality Attributes 15. American Elsevier, 1978. We had never gotten a completely satisfactory architecture presentation from the architect. 18.8 Discussion Questions 1. Stateless. As this book was being prepared for publication, companies around the world were learning to cope with remote participation and work-from-home practices due to the COVID-19 crisis. To inform the applications that the device is about to shut down, the applications must register with the battery manager. Manage Resources A resource manager is a speci c form of intermediary that governs access to computing resources; it is similar to the restrict communication paths tactic. A couple of times we began an evaluation, only to lose the architect in the middle of the exercise. 21.3 Who Can Perform the Evaluation? Concurrency. It also means that new features do not need to be bundled into a release, but can be put into production at any time. If so, then the number of qubits available will grow exponentially over time. [Wood 07] W. Wood. We use your credit card to renew your subscription automatically. Some design concepts, such as patterns, are extensively documented; others, such as externally developed components, are documented in a less thorough way. We present a few that are among the most commonly used here. Fixed-priority scheduling assigns each source of resource requests a particular priority and assigns the resources in that priority order. Service-oriented systems that utilize dynamic service discovery and binding also exhibit these properties. Organizations may not be able to hire developers at a single location: Relocation costs may be high, the size of the developer pool may be small, or the skill sets needed may be specialized and unavailable in a single location. Around the same time, Brian Oki and Barbara Liskov independently developed and published an algorithm called Viewstamped Replication that was later shown to be equivalent to Lamports Paxos [Oki 88]. What new architecture? I asked blankly, and out it came. B. Bondi. [Bouwers 10] E. Bouwers and A. van Deursen. Addison-Wesley, 2016. Alternative requests. What kind of bandwidth, latency, or jitter can be expected for a given connector? Usually we dont proceed without the architect, but it was okay, because the architects apprentice stepped in. In fact, if functionality were the only thing that mattered, you wouldnt have to divide the system into pieces at all: A single monolithic blob with no internal structure would do just ne. 8. Use an intermediary is a modi ability tactic. Which stakeholders will participate? We calculated the average bug xes per le annually for the total project as 0.33. A context diagram shows how the system or portion of the system relates to its environment. Fortunately, it is possible to make quality predictions about a system based solely on an evaluation of its architecture. The model for analyzing debt identi es areas of the architecture that are experiencing unusually high rates of bugs and churn (committed lines of code) and attempts to associate these symptoms with design aws. 179188. For example, if you are designing a web application that needs to communicate with an external application to handle payments, you will probably need to add an integration component alongside the traditional presentation, business, and data tiers. The second category includes those that describe some property of the development of the system, such as modi ability, testability, or deployability. Bene ts: The cost of certifying the system is reduced because you need to certify only a (usually small) portion of the total system. Tactics and patterns that are more desirable for a particular problem should improve the resulting design solution, perhaps by making it easier to arbitrate con icting design constraints, by increasing insights into poorly understood design contexts, and by helping surface inconsistencies in requirements. Pearson+ is a collection of learning tools, videos and eTextbooks that help you learn how you learn best. Abstract Common Services Where two elements provide services that are similar but not quite the same, it may be useful to hide both speci c elements behind a common abstraction for a more general service. What impact does the use of locks have on other quality attributes? Code on demand (optional). [Garlan 95] David Garlan, Robert Allen, and John Ockerbloom. Find examples of projects that have undergone major refactorings. Pattern-Oriented Software Architecture Volume 3: Patterns for Resource Management. An organizationlevel skill might be e ective knowledge management or human resource management as applied to architects. FTA is a top-down deductive approach to identify failures that could result in moving the system into an unsafe state. Changes in the elements state brought about by using the resource. If two elements need to interact, have them exchange as little information as possible. Most operations also return a result. Tactics in this categorymanage event arrival, limit event response, prioritize events (perhaps letting low-priority events go unserviced), reduce computational overhead, bound execution times, and increase resource usage e ciencyall directly increase energy e ciency by doing less work. 26.2 Quantum Teleportation Recall that it is not possible to copy one qubit to another directly. (See the Scheduling Policies sidebar.) Upward usages are not allowed in this pattern. A work ow is a set of organized activities that order and coordinate software components to complete a business process. The functional redundancy tactic is still vulnerable to speci cation errorsand, of course, functional replicas will be more expensive to develop and verify. Mobile Sensors and Context-Aware Computing. For example, systems are frequently (always?) For example, electricians, plumbers, heating and air conditioning specialists, roofers, and framers are each concerned with di erent structures in a building. Do Not Sell Or Share My Personal Information, 1.4 Fundamental Security Design Principles, 1.8 Key Terms, Review Questions, and Problems, 2.1 Confidentiality with Symmetric Encryption, 2.2 Message Authentication and Hash Functions, 2.4 Digital Signatures and Key Management, 2.6 Practical Application: Encryption of Stored Data, 2.7 Key Terms, Review Questions, and Problems, 3.1 Digital User Authentication Principles, 3.6 Security Issues for User Authentication, 3.7 Practical Application: An Iris Biometric System, 3.8 Case Study: Security Problems for ATM Systems, 3.9 Key Terms, Review Questions, and Problems, 4.7 Identity, Credential, and Access Management, 4.10 Key Terms, Review Questions, and Problems, 5.9 Key Terms, Review Questions, and Problems, 6.2 Propagation Infected Content - Viruses, 6.3 Propagation Vulnerability Exploit - Worms, 6.4 Propagation Social Engineering SPAM E-Mail, Trojans, 6.6 Payload Attack Agent Zombie, Bots, 6.7 Payload Information Theft Keyloggers, Phishing, Spyware, 6.8 Payload Stealthing Backdoors, Rootkits, 6.10 Key Terms, Review Questions, and Problems, 7.3 Distributed Denial-of-Service Attacks, 7.6 Defenses Against Denial-of-Service Attacks, 7.7 Responding to a Denial-of-Service Attack, 7.8 Key Terms, Review Questions, and Problems, 8.6 Distributed or Hybrid Intrusion Detection, 8.10 Key Terms, Review Questions, and Problems, 9.2 Firewall Characteristics and Access Policy, 9.7 Example: Unified Threat Management Products, 9.8 Key Terms, Review Questions, and Problems, 10.4 Key Terms, Review Questions, and Problems, 11.4 Interacting with the Operating System and Other Programs, 11.6 Key Terms, Review Questions, and Problems, 12.1 Introduction to Operating System Security, 12.9 Key Terms, Review Questions, and Problems, 13.6 Key Terms, Review Questions, and Problems, 14.2 Organizational Context and Security Policy, 14.7 Key Terms, Review Questions, and Problems, 15.1 IT Security Management Implementation, 15.7 Key Terms, Review Questions, and Problems, 16.3 Physical Security Prevention and Mitigation Measures, 16.4 Recovery from Physical Security Breaches, 16.5 Example: A Corporate Physical Security Policy, 16.6 Integration of Physical and Logical Security, 16.7 Key Terms, Review Questions, and Problems, 17.1 Security Awareness, Training, and Education, 17.4 Computer Security Incident Response Teams, 17.5 Key Terms, Review Questions, and Problems, 18.5 Security Information and Event Management, 18.6 Key Terms, Review Questions, and Problems, 19.5 Key Terms, Review Questions, and Problems, Appendix 19A: Information Privacy Standard of Good Practice, 20.1 Symmetric Encryption and Message Confidentiality, 20.8 Key Terms, Review Questions, and Problems, 21.4 The RSA Public-Key Encryption Algorithm, 21.5Diffie-Hellman and Other Asymmetric Algorithms, 21.6 Key Terms, Review Questions, and Problems, 22.3 Secure Sockets Layer (SSL) and Transport Layer Security (TLS), 22.6 Key Terms, Review Questions, and Problems, 23.5 Key Terms, Review Questions, and Problems, 24.5 Key Terms, Review Questions, and Problems, Appendix A Projects and Other Student Exercises for Teaching Computer Security, A.11 Webcasts for Teaching Computer Security. 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