Using Model Frameworks

Model-only Strategy. In this strategy, you build and use model frameworks. 

The frameworks approach also works at the level of problem domain models. The ideal approach is to formulate requirements themselves in a modular fashion by using model frameworks and plugging in the specifics for your problem implementing a code framework solution to the generic problem specification and specializing that implementation framework to construct your system. A typical system consists of numerous such code frameworks and demands careful use of component-based techniques—such as event protocols across frameworks—so that the parts work together correctly. 

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. ... 

Catalysis uses model frameworks for extensibility stereotypes are only one special (and limited) syntax for applying a framework. 

The best modeling framework for R D options is, however, more contentious. The famous, or infamous, Black-Scholes formula [8], based on valuation of traded hnancial options, has in our view impeded the practical use of decision analysis methods by scientihc managers ... 

The development of the differential equations which describe the evolution of particle size and molecular weight properties during the course of the polymerization is based on the so-called "population balance" approach, a quite general model framework which will be described shortly. Symbols which will be used in the subsections to follow are all defined in the nomenclature. 

A valid mechanistic model can be very useful, not only in that it can appreciably add to our process understanding, but also in that it can be successfully employed in many aspects of emulsion polymerization reactor technology, ranging from latex reactor simulation to on-line state estimation and control. A general model framework has been presented and then it was shown how it can be applied in a few of these areas. The model, being very flexible and readily expandable, was further extended to cover several monomer and comonomer systems, in an effort to illustrate some of its capabilities. 

The framework is applied twice, with placeholder names substituted as indicated. Each substitution for defines a derived type Use. The framework applications can be unfolded to reveal the complete model. The benefits of frameworks are that they simplify a picture, and, having been tried and tested, they often deal with matters you might not have thought of (such as the possibility of a Room being closed). The details and precise specifications have already been worked out for you. 

In general, a component framework is a collaboration in which all the components are specified with type models some of them may come with their own implementations.22 To use the framework, you plug in components that fulfill the specifications. The plug-in implementations may do far more than the spec requires that doesn t matter, provided that... 

We will use the idea of join again when we discuss model frameworks in Chapter 9, Model Frameworks and Template Packages. Partial models kept in libraries can be composed to make complete models their documentation need be kept only in one place. 

Chapter 9, Model Frameworks and Template Packages, shows how recurring patterns of types, collaborations, and refinement can be captured using the idea of a framework a template package. The resulting model can then be used as a skeletal model that is applied with various specializations to different problems. Frameworks enable you to define new modeling constructs. 

Do not lose sight of the domain terms even in your code. Use refinement to maintain trace-ability even as your code becomes more decoupled and reusable. Wherever possible, recast the problem domain descriptions themselves using these orthogonal and more abstract views remember, you are actively constructing a model of reality and not passively discovering it. Use frameworks (see Chapter 9, Model Frameworks and Template Packages) to explicitly document the mapping from domain terms to terms and roles in the abstract problem descriptions. 

This chapter deals with model frameworks and explains how to build and compose them using template packages. It also discusses how the fundamentals of the entire Catalysis approach are themselves defined as such frameworks and shows how they can form the basis for a modeling language that is truly extensible. 

This is where model frameworks are useful. Let s assume that because Observation is a common pattern, we have defined a model framework for it using it gives us an abbreviated way of defining what we need (see Figure 9.1). 

Notice that what the Observation framework does is to represent a cluster of design decisions about how two types of objects should collaborate to provide the required effect. It does not discuss any other roles and collaborations of those objects, and it decouples this design work from any specific domain. This is one of the most effective uses of model frameworks. 

In summary, templates provide a powerful way to capture reusable model frameworks, whether at an abstract specification level or down in the detailed design. In particular, templates are good for capturing collaborations. Even without tools, the template notation is a useful form of abbreviation even when the template is not very rigorously defined. It s an easy way to say on a diagram, This, this, and this type have such-and-such a relationship. ... 

This tells us that a Trader must always have an Order pending for low stock in that way, we hope to avoid outages. Designers might find it convenient to use this framework by itself and then go on to define within their own models how Orders are made. Or we could go on to define another framework that includes that information. 

A model framework is a generic package containing both normal and placeholder definitions. A placeholder is a name that can be substituted when the framework is used. Each use or application of the framework provides its own substitutions of the placeholders. Placeholder names are distinguished with angle brackets (<>). The names of attributes and associations of placeholder types are themselves placeholders. (This is not automatically true of actions.)... 

Model frameworks can be used to express relationships that straddle type boundaries and to encapsulate relationships made up of a collection of types, associations, and actions. They are a powerful tool for abstraction and a useful unit of reuse. 

Chapter 10, Components and Connectors, describes the richness of component-based developmemt and explains how it raises the level at which implementation units can be connected to build larger systems. Because there is no single answer to what constitutes useful component and connection mechanisms, we use frameworks (see Chapter 9, Model Frameworks and Template Packages) to define the generic building blocks of different component architectures. 

Using a model framework, such as resource allocation, to model problems ranging from seminar room allocation to scheduling machine time for production lots in a factory. 

Use a tool that will help you compose model frameworks. 

This list includes all kinds of development work. We have already discussed model frameworks and template packages, which can be valuable to an enterprise. They are white-box assets What you see is what is they offer. By contrast, an executable piece of software, delivered without source code, can perform a useful and well-defined function and yet not be open to internal inspection. Software vendors prefer such black-box components. 

This model framework uses abstract types such as Job, Requirement, and Resource and abstract relationships such as meets, provides, and so on. These types will map in very different ways to a car rental application (Resource=Vehicle, Job=Rental, meets=model category matches) than to assigning instructors to seminars (Resource=lnstructoi Job=Session, meets=instructor qualified for session topic). 

Parts II, III, and IV cover basic techniques for modeling with objects and advanced techniques for factoring and then recombining models and designs using packages, frameworks, and components. They do not describe a development process the steps to validate and document these models. 

Subtyping and model frameworks are used to simplify and generalize the model. 

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