Database Management Systems: Structures and Components

Database Presentation and Form Generation

Systems present data on a screen or printer using a predefined format, or one that is easy to define without requiring knowledge of database languages or programming. This includes form generators and dialogues that display items, allowing for information input via keyboard or buttons.

Data Structure Diagrams

A Data Structure Diagram is a graphic used to represent the design of a database. It utilizes boxes to represent nodes and lines to represent ties or relations, specifying the general logical structure of the database.

Key Terminology

• Path: Lines that connect nodes.
• Segment: A record of a hierarchical database.
• Member: A child record in a networked database.
• Joint: A connection between two record types in a network database.
• Leaves: Nodes without children in a hierarchical database.
• Branch: A line that ends at a leaf in a hierarchical database.
• Owner: A record containing a network database member.
• Parent: A parent record in a networked database.

Operational Structure of the DBMS

The two elements of a database—clients and servers—can run on the same machine or on different computers interconnected by a communication system. Communication between the two is facilitated by SQL query languages and standard network protocols.

Database Architecture Types

Depending on the number of servers and how a client accesses them, there are two primary database structures:

1. Client-Server Architecture

This structure is composed of the client application, the data access layer, and the database server:

• Client Application: Responsible for verifying and accepting user input. It sends requests to the database server, which processes them and returns the results.
• Data Access Layer: Contains an Application Programming Interface (API) responsible for sending queries to the server. This layer is transparent to the user.
• Database Server: Accepts queries from clients, processes them, and returns the results.

2. Multi-Client Architecture

In this model, a client can connect to more than one server simultaneously, or connect to a single server per session. When a client application accesses data from different servers, the system is referred to as a Distributed Database, where data is distributed across multiple machines linked through a network.