Changeability in Model Driven Web Development

ionA view of an object that focuses on the information relevant to a particularpurpose and ignores the remainder of the information.[IEEE Std 610.12-1990]In order to focus on some aspect of a system, or “separate a concern”, other aspects must be left out orhidden. In this context [Booch1993] quotes [Shaw1977]: We (humans) have developed an exceptionallypowerful technique for dealing with complexity. We abstract from it. Unable to master the entirely of anobject, we choose to ignore its essential details, dealing with the generalized, idealized model of theobject. [Shaw1977] describes the use of abstraction in order to focus on certain aspects, a powerfultechnique in dealing with complexity. Besides this focus models also provide a means to separateconcerns and add structure like hierarchies. ModelA model of a system is a description or specification of that system and itsenvironment for some certain purpose. A model is often presented as acombination of drawings and text. The text may be in a modeling languageor in a natural language. [Miller2003] A model is a simplification of a system built with an intended goal in mind.The model should be able to answer questions in place of the actual system.[Bezivin2001]A model is a set of statements about some system under study.[Seidewitz2003] Models are used throughout history for various purposes, e.g. paintings or roadmaps. Examples ofmodels showing different concerns or views of one subject are blueprints of a house showing wiring orplumbing, or maps of a landscape showing altitudes, sorts of ground or climates. Within softwaredevelopment modeling has been used extensively to express parts of the system. Examples of languagesused for this purpose are the Unified Modeling Language (UML), Archimate and the Business ModelingNotation (BPMN). Changeability in model driven web development 61Models can be used in various ways. For example in [Fowler2003] Martin Fowler describes the use ofmodels for sketching, blueprinting and programming. The different purposes have different levels offormality. In MDSD the models are the system, therefore the models must be formal enough to beinterpreted by a computer. The models are used to “program” the application.A models representation can be graphical, textual or a combination of both. Source code can also beseen as a model [Mens2005][ Kleppe2008+ *Favre2004+. Kleppe introduces the term “Mogram” todescribe a product written in a software language. As programming or modeling languages aredescribed by their grammar/metamodel, these also can be seen as models [Favre2004]. MODELING LANGUAGETo create models modeling languages are required. Programming languages are usually textual andconsist of an abstract syntax, a concrete syntax and semantics. Semantics are often not formally defines,and the abstract and concrete syntax are often described intertwined within a grammar, e.g. in acontext free grammar. Textual versus graphical language specification formalisms can be categorized astree versus graph formalisms. Modeling languages are more expressive when able to use both graphicaland textual notations. A separation of abstract and concrete syntax is recommended, because differentnotations for different purposes add a lot of value. The metamodeling formalism provides a way to dothis. For more information on this subject, see [Kleppe2008]. Kleppe states that a metamodel specifies amodeling language, and is usually the model of an abstract syntax.Language descriptions are written in languages, e.g. EBNF. These languages are capable to describelanguages and so are capable of describing themselves. In MDSD these languages are calledmetametamodels. [Bezivin2005] and [Favre2004] introduced the term megamodel to describe themodel that uses concepts as model, metamodel and metametamodel, see figure 1. The layering in thepicture is based on the four-layered architecture of the MOF standard from the OMG. Changeability in model driven web development 62Figure 1 Metamodeling architectureMegamodel