Krishna Structured Query Language, commonly abbreviated to SQL and pronounced as “sequel”, is not a conventional computer programming language in the normal sense of the phrase. It allows users to access data in relational database management systems. SQL is about data and results, each SQL statement returns a result, whether that result be a query, an … Read more
Once entities and relationships have been identified and defined, the first draft of the entity relationship diagram can be created. This post introduces the ER diagram by demonstrating how to diagram binary relationships. Recursive relationships are also shown. Binary Relationships Figure 1 shows examples of how to diagram one-to-one, one-to-many, and many-to- many relationships. Figure … Read more
The data model is one part of the conceptual design process. The other is the function model. The data model focuses on what data should be stored in the database while the function model deals with how the data is processed. To put this in the context of the relational database, the data model is … Read more
The Entity-Relationship (ER) model was originally proposed by Peter in 1976 as a way to unify the network and relational database views. Simply stated the ER model is a conceptual data model that views the real world as entities and relationships. A basic component of the model is the Entity-Relationship diagram which is used to … Read more
Database design is defined as: “design the logical and physical structure of one or more databases to accommodate the information needs of the users in an organization for a defined set of applications”. The design process roughly follows five steps: 1. Planning and analysis 2. Conceptual design 3. Logical design 4. Physical design 5. Implementation … Read more
A data model is a conceptual representation of the data structures that are required by a database. The data structures include the data objects, the associations between data objects, and the rules which govern operations on the objects. As the name implies, the data model focuses on what data is required and how it should … Read more
Several criteria are normally used to classify DBMSs. The first is the data model on which the DBMS is based. The main data model used in many current commercial DBMSs is the relational data model. The object data model was implemented in some commercial systems but has not had widespread use. Many legacy (older) applications … Read more
Three important characteristics of the database approach are (1) insulation of programs and data (program-data and program-operation independence); (2) support of multiple user views; and (3) use of a catalog to store the database description (schema). In this post we specify an architecture for database systems, called the three-schema architecture, which was proposed to help … Read more
A primary goal of a database system is to retrieve information from and store new information in the database. People who work with a database can be categorized as database users or database administrators. Database Users and User Interfaces There are four different types of database-system users, differentiated by the way they expect to interact … Read more
We can define a data dictionary as a DBMS component that stores the definition of data characteristics and relationships. You may recall that such “data about data” were labeled metadata. The DBMS data dictionary provides the DBMS with its self describing characteristic. In effect, the data dictionary resembles and X-ray of the company’s entire data … Read more