A database schema can be defined as a visual representation of a database, the set of governing rules of a database, or the complete set of objects that a specific user utilizes. Data modeling is the process of creating such systems. Usually, a database designer creates the schema for the purpose of assisting the programmers of a piece of software that will engage with the database. Basically, the database schema displays a graphical view of the database architecture. With this, it allows for a means of showing and grouping objects within the database such as relations, functions, fields, and tables.
Difference Between Instances and Schemas
While these terms are related, there are important distinctions between them. It is important to note that a database schema does not actually contain any data. It is simply a skeleton of a planned database. On the contrary, a database instance contains data and is an image of a database as it existed at a specific point in time. Therefore, database instances are adaptable. They can be changed to different reference points whereas schemas are unchanging due to the extreme difficulty of their alteration once in operation. These two types of databases affect each other using a database management system. This system abbreviated as DBMS enforces compliance between the constraints of the schema and the structures of the instance.
Different Types of Database Schema
There are distinct patterns and norms used within database design that define this term. The simplest and most common of these patterns is known as the “star schema”. With the star system, best for managing less complex queries, one or multiple fact tables can be linked to a number of dimensional tables. Conversely, the “snowflake schema” is used for more complex and multidimensional databases. Within the snowflake pattern, the dimensions are standardized into many unique tables that connect to one another creating a system similar to the structure of a snowflake.
Database schema plays an important role in the Oracle database system. However, within the Oracle system, the term has a slightly different meaning and usage. The schema, known as “SQL schema” is a database that can contain multiple schemata. Each schema houses the user-created objects. In Oracle, the objects can include views, synonyms, tables, and more. Some objects, however, are restricted, like contexts, directory objects, roles, and users.