Logical design is based on the logical level model and is a description and construction of link diagrams between data elements, regardless of their content and storage environment.
The logical structure of the database (Fig. 1) is obtained by converting the conceptual schema into a logical schema (model) oriented to the selected DBMS.
With regard to the most common relational data model, the general approach to converting a conceptual schema into a logical one is that each entity, which is a representative of a set of objects of the same type, is defined as a schema of a separate relationship (table), and the attributes of the entity form the columns of the table. The primary key of an entity forms the original primary key of the table, which can be changed later.
Designing the logical structure of the database should solve the problem of choosing the most efficient data structure, providing quick access to data; elimination of data duplication, ensuring data integrity in such a way that when some objects are changed, a corresponding change in related objects automatically occurs.
Fig.1 – Logical model of the database
Physical model of the database
The logical domain data model (business components) provides developers with an understanding of data structures. After its development, one should start modeling the physical structure of the storage systems of the identified data objects, that is, the development of a physical data model.
The structural diagram is important for both the database developer and the end user. It allows you to visually consider the input data of the project being developed. This, in turn, allows the developer to better understand the meaning of the work and, accordingly, create a better product. Thanks to the structural diagram, the end user will quickly and better understand the logic of the created database, which, of course, will affect the quality of the work done by the user.
At the development stage, it is necessary to create a structural diagram of the automation object, which is built on the basis of the input data, if the conceptual model is not yet ready. This scheme is necessary, first of all, so that the developer at the initial stages of development can clearly understand the database model, as well as how to implement the project as a whole and its individual parts. At the subsequent stages – to make changes to existing components, create new components and delete old ones if they are no longer needed or replaced by others, and, finally, the scheme is needed in order to develop the most efficient database.
Table office equipment
2.5 Development of the program module algorithm
The development of the program structure is based on the organization of an object-oriented interface, which uses a user interaction model focused on manipulating objects of the subject area. Within this model, the user is given the opportunity to directly interact with each object and initiate the execution of operations during which several objects interact. The user’s task is formulated as a purposeful change of some object that has an internal structure, a certain content and an external symbolic or graphical representation. In this case, the object is understood in the broad sense of the word, for example, a model of a real system or process, a database.