computer security: principles and practice 4th edition githubcomputer security: principles and practice 4th edition github

Whenever contention for a resource occurs, the resource must be scheduled. If you get wind of a change to the ASRs, you can take preliminary steps to design for it, as an exercise to understand the implications. The lesson here is that if you are the architect for software that resides in a physical system, you will need to understand the QAs that are important for the entire system to achieve, and work with the system architects and engineers to ensure that your software architecture contributes positively to achieving them. What are the disadvantages? Earliest-deadline- rst assigns priorities based on the pending requests with the earliest deadline. [Bruntink 06] Magiel Bruntink and Arie van Deursen. Is there a di erent de nition of software architecture that you are familiar with? Surely not all of them. 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. Thus, all C&C structures are orthogonal to the module-based structures and deal with the dynamic aspects of a running system. The hostname returned after allocating a VM re ects the fact that the IP address has been added to the cloud Domain Name System (DNS). Event bus. high-technology firms. Viewstamped Replication: A New Primary Copy Method to Support Highly-Available Distributed Systems, PODC 88: Proceedings of the Seventh Annual ACM Symposium on Principles of Distributed Computing, January 1988, pp. Using an energy discovery service in a cloud context, or a controller in a multi-core context, a computational task can dynamically switch among computational resources, such as service providers, selecting the ones that o er better energy e ciency or lower energy costs. Organizing for Software Product Lines, Proceedings of the 3rd International Workshop on Software Architectures for Product Families (IWSAPF3), pp. . Hedged requests. PCC 2.5 Early Design Decisions Software architecture is a manifestation of the earliest design decisions about a system, and these early bindings carry enormous weight with respect to the systems remaining development, its deployment, and its maintenance life. Documenting an Architecture 23. Virtually all software systems change over their lifetimes, to accommodate new features, to adapt to new environments, to x bugs, and so forth. Memento The memento pattern is a common way to implement the undo tactic. Finally, the execution time for a request is limitedyour service must process the request and exit within the providers time limit or it will be terminated. 7.2 General Scenario for Integrability Table 7.1 presents the general scenario for integrability. The 2014 paper subsequently inspired [Paradis 21]. Research the o erings of a major cloud provider. Communication links, by comparison, may not have authorization controls. Researchers focusing on humancomputer interactions have used the terms user initiative, system initiative, and mixed initiative to describe which of the human computer pair takes the initiative in performing certain actions and how the interaction proceeds. Using a standard presentation, the leader describes the ATAM steps in brief and the outputs of the evaluation. Transactions. This will allow increments to be planned, which is critical in any project that hopes to release its software incrementally. How much information is transferred and at what rate? Mobile vehicle systems tend to have relatively long lifetimes. The deployment introduces no defects and no SLA is violated. Figure 5.1 Sample concrete deployability scenario 5.4 Tactics for Deployability A deployment is catalyzed by the release of a new software or hardware element. Exam make-ups are not allowed (early or late). Stakeholders can allocate any number of their votes to any scenario or combination of scenarios. Second, we are always honest. These compositions have been found to be useful over time and over many di erent domains, so they have been documented and disseminated. We will examine a bakers dozen of the most important reasons. Is it possible to intercept the exchanged messages and easily observe their content? Storey, K. Wong, and H. Mller. Tradeo s: Dependency injection makes runtime performance less predictable, because it might change the behavior being tested. Another approach is to use testers from within the organization that is developing the software. 12.7 Discussion Questions 1. For example, in Figure 22.4, the transitions correspond to the buttons the driver can press or driving actions that a ect the cruise control system. Resist Attacks There are a number of well-known means of resisting an attack: Identify actors. XML schemas enable you as an architect to specify a rich information structure. Such personnel or systemsthe set of relevant actorsmust be noti ed when the system has detected an attack. The usefulness of ADLs lies in their ability to support automation through associated toolsautomation to provide useful analysis of the architecture, or assist in code generation. The VM Images section discusses this process in more detail. 3. This is, for some programmers, their primary performance tactic. In the Risk column indicate the risk of implementing the tactic using a (H = High, M = Medium, L = Low) scale. In addition to creating and destroying VMs, the hypervisor monitors them. Frank Gehry Any practice of architecture performed outside of a classroom takes place in the larger context of a development project, which is planned and carried out by people working in one or more organizations. The management gateway is responsible for tens of thousands of physical computers, and each physical computer has a hypervisor that manages the VMs on it. Resources have physical characteristics such as size and weight, have processing capabilities, and carry a cost. Facilitators help the stakeholders put the scenarios in the six-part scenario form of sourcestimulusartifactenvironmentresponseresponse measure that we described in Chapter 3. For example, suppose your build process fetches the latest version of a library. The software elements come from a module or C&C view. Admittedly, we are somewhat biased. In all modern systems, elements interact with each other by means of interfaces that partition details about an element into public and private parts. Split module. A physical computer has a xed amount of physical memory. What set of services would it make sense to group into a Pod (as was done with service meshes) and why? In the gure, the arrows mean leads to. The solid arrows highlight the relationships of greatest interest to architects. 6.5 For Further Reading The rst published set of energy tactics appeared in [Procaccianti 14]. 1.4 Summary 1.5 For Further Reading 1.6 Discussion Questions 2. 5 (2018). Stimulus 3. Memory management hardware partitions a processs address space into pages, and swaps pages between physical memory and secondary storage as needed. If architects arent paying attention to the modularity of their system (and, no, microservices are not a panacea here), that system will quickly become an anchorhard to understand, change, debug, and modify, and weighing down the business. Any number of lters can be de ned and applied, in an arbitrary order, to the request before passing the request to the eventual service. Usually this information is captured in the front matter. The states may also specify entry and exit actions. Next, because the instance may be in the process of servicing a request, the autoscaler must notify the instance that it should terminate its activities and shut down, after which it can be destroyed. As with much of the discussion of quantum computers, QRAM is in the theoretical discussion stage rather than the engineering phase. Step 7: Brainstorm and Prioritize Scenarios The evaluation team asks the stakeholders to brainstorm quality attribute scenarios that are operationally meaningful with respect to the stakeholders individual roles. The following tactics can be used to bind values at compile time or build time: Component replacement (for example, in a build script or make le) Compile-time parameterization Aspects The following tactics are available to bind values at deployment, startup time, or initialization time: Con guration-time binding Resource les Tactics to bind values at runtime include the following: Discovery (see Chapter 7) Interpret parameters Shared repositories Polymorphism Separating the building of a mechanism for modi ability from the use of that mechanism to make a modi cation admits the possibility of di erent stakeholders being involvedone stakeholder (usually a developer) to provide the mechanism and another stakeholder (an administrator or installer) to exercise it later, possibly in a completely di erent life-cycle phase. [Brown 10] N. Brown, R. Nord, and I. Ozkaya. For example, if the architect cannot characterize the number of clients and cannot say how load balancing will be achieved by allocating processes to hardware, there is little point in proceeding to any performance analysis. In this chapter, we have said that architecture documentation is produced in service of architecture stakeholders. Voting also depends critically on having multiple sources to evaluate. 8. The notations original use case was to send JavaScript objects between a browser and web serverfor example, to transfer a lightweight data representation to be rendered as HTML in the browser, as opposed to performing the rendering on the server side and having to download more verbose views represented using HTML. [Nygard 18] Michael T. Nygard. Package dependencies. Dynamic priority scheduling. In the worst case it will yield an approach that simply does not predictably achieve the desired energy e ciency goals. . No, I mean what does the system do, interrupted the questioner. 4 (April 2020): 9598. The collected information from the evaluation is summarized and presented to stakeholders. 15. Once the picture is begun, other decisions are immediately made: Where is the rst line, what is its thickness, what is its shape? 1.1 What Software Architecture Is and What It Isnt There are many de nitions of software architecture, easily discoverable with a web search, but the one we like is this: The software architecture of a system is the set of structures needed to reason about the system. The higher the cohesion, the lower the probability that a given change will a ect multiple modules. As we have said, the organizational and work-breakdown structure of a project is almost always based on its architecture. Di erent classes of users, and their characteristics, need to be identi ed up front. The U.S. National Institute of Science and Technology (NIST) is considering a variety of di erent quantum-based communication protocols to be the basis of a transport protocol called HTTPQ, which is intended to be a replacement for HTTPS. 12). Decisions made to achieve one of the driving architectural requirements should be subject to more analysis than others, because they will shape critical portions of the architecture. What is architectures role in project risk reduction? Creating an Architectural Vision: Collecting Input, July 25, 2000, bredemeyer.com/pdf_ les/vision_input.pdf. A set of identi ed sensitivity points and tradeo points. This will likely follow the same arc as machine languages for classical computers. Thus, a small di erence in the price of a processor multiplied by the millions of copies of the system in which that processor is embedded can make a signi cant di erence to the pro tability of the organization producing the system. Bene ts: Publishers and subscribers are independent and hence loosely coupled. While during XMLs heyday the argument was often made that XML is human readable, today this bene t is cited far less often. Security is a QA that is especially sensitive to processes that take place in the physical world outside the computer: processes for applying patches, processes for choosing and safeguarding your passwords, processes for physically securing the installations where computers and data live, processes for deciding whether to trust a piece of imported software, processes for deciding whether to trust a human developer or user, and so forth. The architects interest in functionality is how it interacts with and constrains other qualities. 3. Architecture documentation can be seen as both prescriptive and descriptive. I much prefer using the word responsibility to describe computations that a system must perform. A structure is simply a set of elements held together by a relation. Dont limit yourself to just your organization. Bonnie John and Len Bass have investigated the relation between usability and software architecture. It provides the system operator with a timely and accurate system status and allows for an appropriate repair strategy to be employed. It is managed through a management gateway that is accessible over the Internet and is responsible for allocating, deallocating, and monitoring VMs, as well as measuring resource usage and computing billing. [Gray 93] Jim Gray and Andreas Reuter. Many systems are built as skeletal systems that can be extended using plug-ins, packages, or extensions. Table 25.4 Knowledge Areas of a Software Architect What about Experience? Using a system e ciently. Choose an agile method and discuss ADD in that context. The message usually maps to a resource (operation) in the interface of the receiver instance. The root of the tree is a successful attack, and the nodes are possible direct causes of that successful attack. When is roll forward a poor choice? MBSE is the formalized application of modeling to support (among other things) system design. Table 15.1 lists the ve most important commands in HTTP and describes their relationship to the traditional CRUD (create, read, update, delete) database operations. Unlike the rest of us, software typically makes the trip many times, as changes and updates are made. Smartphone displays must be large enough for a human to read; automobiles are constrained by weight limits on roads; trains are constrained by track width; and so forth. There may be public read-only interfaces for anonymous actors and private interfaces that allow authenticated and authorized actors to modify the state of an element. Once the risks have been identi ed, then xing them is, like the evaluation itself, a cost/bene t issue. A discovery service may be used to enumerate variants of particular elements that are used in di erent products. But architectures are created by architects working in organizations that are full of actual human beings. An attack tree, which is similar to the fault tree discussed in Chapter 4, is used by security engineers to determine possible threats. If unhealthy inheritance is present, some functionality needs to be moved, typically from a child class to a parent class. Conversely, if you choose to drop events, then you need to choose a policy: Do you log the dropped events, or simply ignore them? De ning Interfaces Interfaces establish a contractual speci cation that allows elements to collaborate and exchange information. If no distribution will occur (that is, if the system is implemented on a single processor), then the deployment structure is trivial and need not be considered further. Addison-Wesley, 2006. Figure 8.2 Goal of modi ability tactics To understand modi ability, we begin with some of the earliest and most fundamental complexity measures of software designcoupling and cohesion which were rst described in the 1960s. The operational performance metrics monitored are used to predict the onset of faults; examples include the session establishment rate (in an HTTP server), threshold crossing (monitoring high and low watermarks for some constrained, shared resource), statistics on the process state (e.g., in-service, out-of-service, under maintenance, idle), and message queue length statistics. Indeed, as we observe experienced architects going about their duties, we notice that the rst thing they do is start talking to the important stakeholders. The SoftServe case study was published in [Kazman 15]. A high-priority event stream can be dispatchedassigned to a resource only if that resource is available. 3. Symphony: View-Driven Software Architecture Reconstruction, Proceedings of the 4th Working IEEE/IFIP Conference on Software Architecture (WICSA 2004), June 2004, Oslo, Norway. In Chapter 20, we show how to integrate all of your drivers, including quality attribute decisions, into a coherent design. For example, suppose you display control buttons on your screen, with the layout speci ed in HTML and CSS, and suppose its automatically generated for all display devices you anticipate using. Proxy servers are able to serve up often-requested web pages, such as a companys home page, without bothering the real application servers that carry out transactions. For example, to build a security driver, you might employ a security pattern, a security tactic, a security framework, or some combination of these. Many times, two possible alternatives do not di er dramatically in their consequences. So you should feel some comfort in knowing that when you try to improve the performance of your computer-based system, you are applying tactics that have been thoroughly road tested. RK 9.3 Tactics-Based Questionnaire for Performance Based on the tactics described in Section 9.2, we can create a set of tactics-inspired questions, as presented in Table 9.2. Examples of qubit operations include the following: 1. 26.7 For Further Reading General overview: Programming Quantum Computers by Eric Johnston, Nic Harrigan, and Mercedes Gimeno-Segovia discusses quantum computing without reference to physics or linear algebra [Johnston 19]. Typical schemes include the following: Replication is the simplest form of voting; here, the components are exact clones of each other. ADD provides detailed guidance on the steps that need to be performed inside each iteration. When you purchase an eTextbook subscription, it will last 4 months. Failure may cause deaths, usually with loss of the airplane. Design and build a little infrastructure to support a little end-toend functionality; repeat until done. Sometimes there was a stack of class diagrams or vague text descriptions masquerading as an architecture. For each parameter, enumerate the architectural characteristics (and the mechanisms to achieve those characteristics) that can a ect this parameter. How does data progress through the system? In an incremental design context comprising multiple rounds, the purpose for a design round may be, for example, to produce a design for early estimation, to re ne an existing design to build a new increment of the system, or to design and generate a prototype to mitigate certain technical risks.

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