Database design

The database design process consists of a number of steps. The general aim of a database design process is to develop an efficient, high-quality database that meets the needs and demands of the application and business stakeholders. Once you have a solid design, you can build the database quickly. In most organizations, database architects and database administrators (DBAs) are responsible for designing a database. Their responsibility is to understand the business and operational requirements of an organization, model the database based on these requirements, and establish who will use the database and how. They simply take the lead on the database design project and are responsible for the management and control of the overall database design process.

The database design process can usually be broken down into six phases, as follows:

• The requirement collection and analysis phase
• The conceptual design phase
• The logical design phase
• The physical design phase
• The implementation and loading phase
• The testing and evaluation phase

These phases of design do not have clear boundaries and are not strictly linear. In addition, the design phases might overlap, and you will often find that due to real-world limitations, you might have to revisit a previous design phase and rework some of your initial assumptions.

The requirement collection and analysis phase

In this phase, you interview the prospective users, gather their requirements, and discuss their expectations from the new database application. Your objective in this phase is to gather as much information as possible from potential users and then document these requirements. This phase results in a concise set of user and functional requirements, which should be detailed and complete. Functional requirements typically include user operations that need to be applied to the database, information flow, type of operation, frequency of transactions, and data updates. You can document functional requirements using diagrams, such as sequence diagrams, data flow diagrams (DFDs), scenarios, and so on.

Moreover, you can also conduct an analysis of the current operating environment—whether it's manual, a file processing system, or an old DBMS system—and interact with users extensively to analyze the nature of the business to be supported; you can also justify the need for data and databases. The requirement collection and analysis phase can take a significant amount of time; however, it plays a vital role in the success of the new database application. The outcome of this phase is the document that contains the user's specifications, which is then used as the basis for the design of the new database application.

The conceptual design phase

Your goal during the conceptual design phase is to develop the conceptual schema of the database, which is then used to ensure that all user requirements are met and do not conflict. In this step, you need to select the appropriate data model and then translate the requirements that arise from the preceding phase into the conceptual database schema by applying the concepts of the chosen data model, which does not depend on RDBMS. The most general data model used in this phase is the entity-relationship (ER) model, which is usually used to represent the conceptual database design. The conceptual schema includes a concise description of the user's data requirements, including a detailed description of the entity types, relationships, and constraints.

The conceptual design phase does not include the implementation details. Thus, end users can easily understand them, and they can be used as a communication tool. During this phase, you are not concerned with how the solution will be implemented. In the conceptual design phase, you only make general design decisions that may or may not hold when you start looking at the technologies and project budget available. The information you gather during the conceptual design phase is critical to the success of your database design.

The logical design phase

During the logical design phase, you map the high-level, conceptual, entity-relationship data model into selected RDBMS constructs. The data model that is chosen will represent the company and its operations. From there, a framework of how to provide a solution based on the data model will be developed. In this phase, you also determine the best way to represent the data, the services required by the solution, and how to implement these services. The data model of a logical design will be a more detailed framework than the one developed during the conceptual design phase. This phase provides specific guidelines, which you can use to create the physical database design.

You do little, if any, physical implementation work at this point, although you may want to do a limited prototyping to see whether the solution meets user expectations.

The physical design phase

During the physical design phase, you make decisions about the database environment (database server), application development environment, database file organization, physical database objects, and so on. The physical design phase is a very technical stage in the database design process. The result of this phase will be a physical design specification that will be used to build and deploy your database solution.

The implementation and loading phase

During this phase, you implement the proposed database solution. The phase includes activities such as the creation of the database, the compilation and execution of Data Definition Language (DDL) statements to create the database schema and database files, the manual or automatic loading of the data into a new database system from a previous system, and finally, the configuration of the database and application security.

The testing and evaluation phase

In this phase, you perform the testing of your database solution to tune it for performance, integrity, concurrent access, and security restrictions. Typically, this is done in parallel with the application programming phase. If the test fails, you take several actions such as adjusting the performance based on a reference manual, modifying the physical design, modifying the logical design, and upgrading or changing the SQL Server software and database server hardware.

The database design life cycle recap

The following diagram briefly illustrates the database design process: