DBMS

Topics: Data modeling, SQL, Database Pages: 16 (3523 words) Published: January 15, 2014
DATABASE ARCHITECTURE

DATABASE CONCEPTS

Figure 1.1 – Main Concepts of a DBMS

Database is an organized collection of data.

Database management system (DBMS) is a computer program (or more typically, a suite of them) designed to manage a database, a large set of structured data, and run operations on the data requested by numerous users.

Data Manipulation Language (DML) is a family of syntax elements similar to a computer programming language used for inserting, deleting and updating data in a database.

Data Definition Language or Data Description Language (DDL) is a syntax similar to a computer programming language for defining data structures, especially database schemas.

Database schema is a set of formulas (sentences) called integrity constraints imposed on a database.

Metadata refers to "data about data".

Metacontent are defined as the data providing information about one or more aspects of the data, such as:

Means of creation of the data
Purpose of the data
Time and date of creation
Creator or author of the data
Location on a computer network where the data were created
Standards used

Fundamental concepts (types) of Metadata
Structural metadata is about the design and specification of data structures and is more properly called "data about the containers of data". Descriptive metadata is about individual instances of application data, the data content. "data about data content" or "content about content"

Some Examples of Software Modules (DB Manager Program)
Structured Query Language (SQL) server
MySQL Database
FoxPro
Microsoft Access

Data Dictionary is a software utility that catalogs an organization's data resources:
what data exist
where they originate
who uses them
what are their format, etc.
Data dictionary not only tells where the data are located in the database, but also which application programs process the data, and closely coordinates with the DBMS in controlling access to the database.

Data model is a set of concepts that can be used to describe the structure of the database:
data types,
relationships,
and constraints that should hold on the data.
Most data models also include a set of operations for specifying retrievals and updates on the database. 

Database Schema is the description of a database.

Figure 1.2 – Schematic Diagram of a DBMS
THE THREE LEVELS OF ARCHITECTURE

Figure 1.3 – The Three Levels of Architecture

External Level
It is how data is viewed by an individual user. Application programmer uses a HOST LANGUAGE: COBOL, PL/1, C . Embedded in the host language is a DATA SUBLANGUAGE DSL.

Conceptual Level
It is how data is viewed by a community of users. A representation of the entire information content of the database. The conceptual schema is a definition of the view of the total database content. Conceptual schema, in most cases, is the union of external schemas. One can add: security and integrity checks, semantic models and data dictionary.

Internal Level
It is how data is physically stored. The internal view is a low-level representation of the entire database. Internal record, or stored record, is built upon physical records, or pages and blocks. 4GL (Fourth-Generation Programming Language)

A programming language or programming environment designed with a specific purpose in mind, such as the development of commercial business software. It is a programming languages closer to human languages than typical high-level programming languages. Most 4GLs are used to access databases. 4GLs are closer to human language than other high-level languages and are accessible to people without formal training as programmers. They allow multiple common operations to be performed with a single programmer-entered command. They are intended to be easier for users than machine languages (first-generation), assembly languages (second-generation), and older high-level languages (third-generation). All 4GLs are designed...
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