Pattern 15.1 Specify Components

This Chapter has two main parts. Section 14.1, Patterns for Specifying Components, on page 613, describes patterns often useful when building a component specification. Section 14.2 onwards illustrates the construction of a specification for the case study. 

Pattern 14.30, Specify components (p.615) motivates the extra effort involved in separating specification of expected behavior from its implementation. Pattern 14.31, Bridge requirements and specifications (p.617) outlines a pragmatic view of requirements, as stated and understood by a user, and the more precise specifications that a developer might use to understand what must be built. Pattern 14.32, Use-case led system specification (p.619) explains why a use-case driven approach to requirements capture is prudent, but should always be interleaved with tools of more precise specifications. 

Pattern 14.36, Construct a system behavior spec (p.628) — Pattern 14.38, Using state charts in system type models (p.636) describe concrete techniques to build the specification of the system of interest. Pattern 14.39, Specify component views (p.640) and Pattern 14.40, Compose Component views (p.642) explain how to show that separately specified components, when composed together in a particular way, realize the required behavior. 

Often, the context model will yield several classes of user, each with a different view of the system see Pattern 14.39, Specify component views (p.640) and Pattern 14.40, Compose Component views (p.642). 

We have several separately constructed views — Pattern 14.39, Specify component views (p.640). 

Certain plots and graphical presentations are frequently used in multivariate analysis and the most frequently used is perhaps the score plot. This is a two-dimensional scatter plot (or map) of scores for two specified components (PCs), in other words a two-dimensional version of Figure 9.32. The plot gives information about patterns in the samples. The score plot for PCI and PC2 may be especially useful because these two components. summarize more variation in the data than any other pair of components. One may look for groups of samples in the score plot and also detect outliers, which may be due to measurement error. In classification analysis the score plot will also show how well the model is able to separate between groups. An example is given in Section 10.4.3. 

In real-time coordination patterns, roles are used to abstract from the actual components participating in one coordination pattern. This way, it is possible to specify and verify coordination patterns independently from other coordination patterns and component definitions and therefore to reduce complexity. In Figure 2 the participating roles of the Registration pattern are registrar and registree the roles of the Convoy pattern are front and rear. Each role behavior is... 

Meaning The pattern specifies a lower bound O on the MTBF of the components listed in the set C. ... 

Meaning The pattern specifies that each of the components in C shall be composed of redundant sub-components. 

On a larger scale, more-complex models can be used to represent the types of whole systems or components and are usually shown pictorially. In an abstract model, the attributes and their types are chosen to help specify the operations on the component as a whole and, according to good object-oriented analysis practice, are based on a model of the domain. However, anyone who has been involved in practical OOD is aware that the design phase introduces all sorts of extra classes as patterns are applied to help generalize the design, make it more efficient, distribute the design, provide persistence or a GUI, and so on. But we can still retrieve the abstract model from any tme implementation in the same way as for the simpler models. 

The starting point for describing an architecture is to define the kinds of elements that constitute it. At the simplest level, interfaces and implementations are the elements of architecture. Beyond that, concrete implemented elements—specific kinds of buffers, synchronization primitives, coordinators, kits of parts to be assembled—can be specified as types or interfaces more-abstract ones—design patterns, patterns of connectors and components—can be described using model frameworks. It is even possible for certain architectural qualities to be quantified, in a parameterized form, on the framework level. After these elements have been defined, the architecture itself can be described using these as primitives. ... 

Crystal symmetries that entail centering translations and/or those symmetry operations that have translational components (screw rotations and glides) cause certain sets of X-ray reflections to be absent from the diffraction pattern. Such absences are called systematic absences. A general explanation of why this happens would take more space and require use of more diffraction theory than is possible here. Thus, after giving only one heuristic demonstration of how a systematic absence can arise, we shall go directly to a discussion of how such absences enable us to take a giant step toward specifying the space group. 

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