Declarative definition of consistency conditions in erm metaschema

A characteristic feature of most information systems is mainly a procedural, algorithmic way of satisfying the functional requirements of the customer. Solution based on the principles of Model Driven Development (MDD) is more elegant, and, most importantly, flexible. In this case, a declarative model is constructed that describes the required functionality, and a universal program carries out the necessary actions based on this model. Changing the requirements entails only a correction of the model; there is no need to rewrite universal programs that implement the model. The first implementation of the research prototype of the ERM model repository was carried out mainly in the traditional way. The exception was, perhaps, the checks that are performed by the relational DBMS based on the integrity constraints of the repository declared in its schema. The expressive power of the ERM model allows representing all the conditions for the consistency of elements of ERM schemas in the repository metaschema. This prompted researchers of the ERM model to try to implement a mechanism for checking consistency schemas in accordance with MDD. The first step in this direction is to expand the ERM metaschema with appropriate descriptions of the consistency conditions. The second step will be the implementation of a universal verification program. As for the model's metaschema, ideally, it should contain all the constraints on the permissible schemas that the metamodel can reflect. The fact that the ERM model is positioned as one of the richest in descriptive capabilities suggests that using of it as a metamodel will allow reflecting all the additional conditions for the consistency of schemas. It is impossible to present the complete metaschema of the ERM model in the form of a single diagram; this would greatly complicate the process of its perception. The interconnections of the basic structural concepts are presented in a skeleton diagram. A separate diagram is used for each consistency condition. It shows the structural concepts of the skeleton diagram that make up the context of the condition, and those special relationships that, in fact, reflect its essence. To illustrate the declarative principles of defining the consistency conditions, several "simple" such diagrams are given. The examples of the presentation of the consistency conditions in the ERM model metaschema presented in the article demonstrate the possibility of its use as a metamodel. This creates the necessary conditions for applying the MDD approach to the implementation of the schema verification mechanism in the ERM repository. It remains to create a program for the interpretation of the metaschema elements reflecting these conditions.

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