Using PM for system modeling., Relational data model...

Using PM for system modeling.

The possibilities of using databases as a information source , as follows from the above, are determined by knowledge of the model representation of related data at all levels of PM design. On the other hand, the type of concrete PM, the chosen way of classification of the domain, the presence of fundamental semantics, the features of conceptual semantics and many other things predetermine the required professional level of users and the possible scale of application of such a PM. The use of databases should be adequately implemented by the project solution, and only in this case the data samples extracted from the PM can really be considered as information for the purposes of modeling the system.5

The use of databases should be provided in the form of strategic objectives of PM design. Especially the formulation of strategic goals is important in the context of designing, building and using integrated distributed databases in modeling complex systems.

Relational data model.

Such a model has at least two principal advantages in comparison with other data models (tree, network). First, the RMD provides a representation of the DB in the form of day-to-day and customary two-dimensional tables, regardless of how the computer is implemented. Thus, the relational model is convenient and obvious. Secondly, the relational database from the mathematical point of view is represented by a finite set of finite relations of different arities. Algebraic operations can be performed on the relations of the model. We can say that thus the theory of relational databases becomes a field of application of mathematical logic and modern algebra and is based on an exact mathematical formalism. In other words, the second advantage of the relational model is the mathematical severity of its definition.

The relational model is homogeneous, since all data is stored in a table with a fixed format of strings that correspond to data about objects and processes in the domain. Obviously, the homogeneity of the relational model does not extend to the essence of the data tables stored in the rows, of course, if the database was not designed using the full technological scheme of the extended relational approach. The mathematical formalism of the relational model is based on the use of the apparatus of modern relational algebra.

The theoretical foundations of the construction of systems of relational calculus are usually hidden behind relatively simple and understandable users (the developers of the machine model M and of systems 5) by the syntactic constructions of formulating queries to B DM. At the same time, the exact classification of a language of manipulation, and therefore of its capabilities and limitations, especially in the context of an extended relational approach, will often require consideration of the theoretical principles and mechanisms laid down in the basis of such a language.

Object-oriented approach and B DM.

In the modern view, the object-oriented approach (OP - the object approach) forms the basis of methodologies for constructing complex systems. The object-oriented approach is related to the representation of the subject domain in the form of classes and objects, which, depending on the purpose of the methodology, can have a different nature. The mapping of the domain of modeling systems S in the form of sets of classes and objects means the implementation of the object model of the representation of systems, which is the key concept of OP. Thus, the object-oriented approach, in fact, is a methodology for constructing methodologies for object modeling of systems. The possibility of applying OD is determined by the ability to represent the subject of modeling (subject area 5) in the form of an object model.

To date, several methodologies have been developed using the OP. First of all, they include the methodology of object-oriented programming (OOP), the implementation of which led to the construction of a number of OOP systems, such as Visual C ++, C ++ Builder, Delphi. The success and high effectiveness of the development of OOP systems is largely due to the fact that the classified objects of the subject areas of programming systems are inherently artificial, have a finite number of known properties and are well abstractable in accordance with the clear classification schemes Mami. The implementation of a fundamentally new programming technology using OOP systems was so effective and that, often, the object-oriented approach proper became identified with object-oriented programming. In fact, this is far from the case, although the lack of good results in applying OT for implementation of other methodologies contributes to the formation of such an opinion.

A special significance of OP is acquired when developing the methodology for constructing object-oriented databases (OODBs). Unlike programming systems, database systems are characterized by a fundamentally different, natural nature of classes and objects of subject areas. The object representation of any subject area of ​​the BMD causes serious problems. Therefore, the informatics section devoted to OODB construction issues is at the initial stage of formation, and many works in this area are limited by the level of assumptions and hypotheses. It seems that it is OP that can be a required way not only to build OODB methodology, but also to develop an object-oriented integration methodology for distributed databases (OODBMS). Obviously, the central problem here is the problem of compositing object-oriented and relational approaches that can lead to the implementation of an extended relational approach along the complete technological scheme (see Figure 5.6).

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