A database management system (or DBMS) is essentially nothing more than a computerized data-keeping system. Users of the system are given facilities to perform several kinds of operations on such a system for either manipulation of the data in the database or the management of the database structure itself. Database Management Systems (DBMSs) are categorized according to their data structures or types. Show There are several types of databases that can be used on a mainframe to exploit z/OS®: inverted list, hierarchic, network, or relational. Mainframe sites tend to use a hierarchical model when the data structure (not data values) of the data needed for an application is relatively static. For example, a Bill of Material (BOM) database structure always has a high level assembly part number, and several levels of components with subcomponents. The structure usually has a component forecast, cost, and pricing data, and so on. The structure of the data for a BOM application rarely changes, and new data elements (not values) are rarely identified. An application normally starts at the top with the assembly part number, and goes down to the detail components. Hierarchical and relational database systems have common benefits. RDBMS has the additional, significant advantage over the hierarchical DB of being non-navigational. By navigational, we mean that in a hierarchical database, the application programmer must know the structure of the database. The program must contain specific logic to navigate from the root segment to the desired child segments containing the desired attributes or elements. The program must still access the intervening segments, even though they are not needed. The remainder of this section discusses the relational database structure. What structures exist in a relational database? Relational databases include the following structures:DatabaseA database is a logical grouping of data. It contains a set of related table spaces and index spaces. Typically, a database contains all the data that is associated with one application or with a group of related applications. You could have a payroll database or an inventory database, for example.TableA table is a logical structure made up of rows and columns. Rows have no fixed order, so if you retrieve data you might need to sort the data. The order of the columns is the order specified when the table was created by the database administrator. At the intersection of every column and row is a specific data item called a value, or, more precisely, an atomic value. A table is named with a high-level qualifier of the owner's user ID followed by the table name, for example TEST.DEPT or PROD.DEPT. There are three types of tables:
Figure 1. Example of a DB2 table (department table) In this table we use:
By creating an index on an employee's name, you can retrieve data more quickly for that employee than by scanning the entire table. Also, by creating a unique index on an employee number, DB2 will enforce the uniqueness of each value. A unique index is the only way DB2 can enforce uniqueness. Creating an index automatically creates the index space, the data set that contains the index. KeysA key is one or more columns that are identified as such in the creation of a table or index, or in the definition of referential integrity.Primary keyA table can only have one primary key because it defines the entity. There are two requirements for a primary key:
The example given is that of an employee's work department number relating to the primary key defined on the department number in the DEPT table. This constraint is part of the definition of the table. What are the elements of database system class 11?Ans. The database management system can be divided into four major components, they are DATA, User, Hardware and Software.
What are the 4 elements of database?The critical elements for creating a database environment are (1) data administration, (2) data-planning and modeling methodology, (3) database technology and management, and (4) users.
What's a database system?Database Systems or DBMS is software that caters to the collection of electronic and digital records to extract useful information and store that information is known as Database Systems/ Database Management Systems or DBMS. The purpose of a standard database is to store and retrieve data.
What are data elements in a database?A basic unit of information that has a unique meaning and subcategories (data items) of distinct value. Examples of data elements include gender, race, and geographic location.
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