Data Elements and Records

Logical Data Elements

• A character is a single alphabetic, numeric, or other symbol.

Data Elements

• A field or data item represents an attribute (characteristic or quality) of an entity (object, person, place, event).
• Examples of fields or data items include salary and job title.

Records

• A record is a grouping of all the fields used to describe the attributes of an entity.
• Example: a payroll record with name, SSN, and pay rate.

Files or Tables

• A file or table is a group of related records.

Databases

• A database is an integrated collection of logically related data elements.

Database Structures

• Common database structures include:

  Types of Database Structures

  • Hierarchical
  • Network
  • Relational
  • Object-oriented
  • Multi-dimensional

Database Structures

• Common database structures include Hierarchical, Network, Relational, Object-oriented, and Multi-dimensional.

Hierarchical Structure

• An early DBMS structure where records are arranged in a tree-like structure.
• Relationships are one-to-many.

Network Structure

• Used in some mainframe DBMS packages.
• Supports many-to-many relationships.

Relational Structure

• The most widely used structure.
• Data elements are stored in tables.
• A row represents a record, while a column is a field.
• Allows relating data in one file with data in another, if both files share a common data element.

Relational Operations

• Select: Create a subset of records that meet a stated criterion, e.g., employees earning more than $30,000.
• Join: Combine two or more tables temporarily, creating a single table that looks like one big table.
• Project: Create a subset of columns in a table.