The most basic logical data element is the character, which consists of a single alphabetic, numeric, or other symbol. One might argue that the bit or byte is a more elementary data element, but we should remember that those terms refer to the physical storage elements provided by the computer hardware.
The next higher level of data is the field, or data item. A field consists of a grouping of related characters. For example, the grouping of alphabetic characters in a person’s name may form a name field (or typically, last name, first name, and middle initial fields), and the grouping of numbers in a sales amount forms a sales amount field. Specifically, a data field represents an attribute (a characteristic or quality) of some entity (object, person, place, or event). For example, an employee’s salary is an attribute that is a typical data field used to describe an entity who is an employee of a business.
All of the fields used to describe the attributes of an entity are grouped to form a record. Thus, a record represents a collection of attributes that describe an entity. An example is a person’s payroll record, which consists of data fields describing attributes such as the person’s name, Social Security number, and rate of pay. File
A group of related records is a data file, or table. Thus, an employee file would contain the records of the employees of a firm. Files are frequently classified by the application for which they are primarily used, such as a payroll file or an inventory file, or the type of data they contain, such as a document file or a graphical image file.
A database is an integrated collection of logically related data elements. A database consolidates records previously stored in separate files into a common pool of data elements that provides data for many applications. The data stored in a database are independent of the application programs using them and of the type of storage devices on which they are stored. Thus, databases contain data elements describing entities and relationships among entities.
The relationships among the many individual data elements stored in databases are based on one of several logical data structures, or models. Database management system packages are designed to use a specific data structure to provide end users with quick, easy access to information stored in databases. Five fundamental database structures are the hierarchical, network, relational, object-oriented, and multidimensional models.
Early mainframe Database Management Structure (DBMS) packages used the hierarchical structure, in which the relationships between records form a hierarchy or treelike structure.
The network structure can represent more complex logical relationships and is still used by some mainframe DBMS packages. It allows many-to-many relationships among records; that is, the network model can access a data element by following one of several paths, because any data element or record can be related to any number of other data elements.
The relational model is the most widely used of the three database structures. It is used by most microcomputer DBMS packages, as well as by most midrange and mainframe systems. In the relational model, all data elements within the database are viewed as being stored in the form of simple two-dimensional tables sometimes referred to as relations. The tables in a relational database have rows and columns. Each row represents a single record in the file, and each column represents a field. 4.
Three basic operations can be performed on a relational database to create useful sets of data. The select operation is used to create a subset of records that meet a stated criterion. 5.
The multidimensional model is a variation of the relational model that uses...
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