DATABASE DESIGN - IBM Mainframe

Database design provides a means to represent the real world entities in a form that can be processed by the computer. Database models present a process of abstracting real world entities into computer representations. They give us methods to capture the static and dynamic attributes of real entities. For example, if we want to capture the attributes of a human being, then we can scan his photograph, finger print him, scan his retina images, get his details like name, ages, sex, height, weight, date of birth, blood group, address, telephone numbers, profession, etc. But the question is how much information about an entity should be collected and represented in the database representation for it to be meaningful and accurate and more importantly useful from the application point of view.

Database Design Process

Database Design Process

To develop a good design one has to understand the meaning of information and the intended use of the information's stored representation within the computer system. Once we develop the understanding and identify the use of information in the application, we can determine how much and what kind of information we require. We can also determine in what format these information should be captured and represented in the computer system or database. During the determination of an application's information requirements it will become apparent which data are essential for the application, which are desirable and which are not needed at all. During this phase it will also become clear that which data entities represent information redundancies and which entities are critical, which are useful and which are not related to the application.

It is important to collect and analyze the static and dynamic information available about the real world application before starting the database design. For evolving a good database design it is important that one uses a model, a database design model. The database design models have the following benefits:

  • They provide a means to represent real world objects in computer usable form.
  • They capture and represent associations and relationships among the real world objects, allowing the application designers to capture the dynamic nature of the real-world enterprise's activities.
  • They define how the objects in the application interact in logical terms.
  • They allow the database designer to capture static and dynamic organization and flow of information within a modeled enterprise.
  • They allow designers and users of the system to better understand the static and dynamic behavior of the system being modeled.
  • They help in improving the maintainability, scalability and reliability of the system.

The determination of the information requirements for an application will play a crucial role in the selection of an actual database structural data model for specification and design.

Static and Dynamic Information

Static and Dynamic Information

Requirements Analysis

To determine how to construct the DBMS for an application, the database design team must first determine the scope of the problem requiring the database system. Requirements Analysis techniques are used to define the scope of the requirements of an applications domain. Requirements Analysis examines the entire scope of the problem domain and includes:

  • Defining the human factors of the application.
  • Defining the application's functionality.
  • Defining all the information managed and used by the application.
  • Determining from where or to where all interfaces to an application derive.
  • Identifying all resource requirements including hardware, software and other physical resources.
  • Deciding on the security requirements and mechanisms.
  • Defining the quality, reliability, performance and operational aspects of the application.

For all these requirements, the analyst must examine the data collected and determine how useful they are for the application. Particularly the information must be analyzed with regard to the following criteria:

  • Correctness - The information should correctly represent the real world system that it is modeling.
  • Consistency - The data should adequately capture the constraints of the real world entity. Once the entity has been defined, we must be certain that the definition covers the entire range of possible values that the entity may take.
  • Completeness - The represented real world entity should not have any missing attributes. All the relevant components of the real world entity should be present in the model.
  • Realistic Representation - The representation of the real world entity should make sense.
  • Need - The information that is being captured should be required for the application.

Information Modeling

The objective of information modeling is to identify the major entities that are fundamental in an application and model them in a target database schema model. In all real world systems there will be a lot of entities, but not all of them will be relevant from the application point of view. So identifying those entities that are really important, relevant and useful for the application is the most important goal of information modeling. The information collected during the requirements analysis stage forms the input for information modeling. This information will enable the database designer to fully and correctly define the major entities to be modeled in the database. The attributes that define the entities of the application are grouped together according to the data model used and stored for further, reference.


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