Text IV database

A database is a structured collection or records or data that is stored in a computer system. The structure is achieved be organizing the data according to a database model. The model in most common us today is the relational model. Other models such as the hierarchical model and the network model use a more explicit representation of relationships.

Depending on the intended use, there are a number of database architectures in use. Many databases use a combination of strategies. On-line Transaction Processing systems (OLTP) often use a row-oriented datastore architecture, while data-warehouse and other retrieval-focused applications like Google’s Big Table, or bibliographic database (library catalogue) systems may use a Column-oriented DBMS architecture.

There are also other types of database which cannot be classified as relational databases.

Database management systems

A computer database relies on software to organize the storage of data. This software is known as a database management system (DBMS). Database management systems are categorized according to the database model that they support. The model tends to determine the query languages that are available to access the database. A great deal of the internal engineering of a DBMS, however, is independent of the data model, and is concerned with managing factors such as performance, concurrency, integrity, and recovery from hardware failures. In these areas there are large differences between products.

A relational Database Management System (RDBMS) implements the features of the relational model outlined above. In this context, Date’s “Information Principle” states: “the entire information content of the database is represented in one and only one way”.

Database models

Products offering a more general data model than the relational model are sometimes classified as post-relational. The data model in such products incorporates relations but is not constrained by the Information Principle, which requires that all information is represented by data values in relations.

Object database models

In recent years, the object-oriented paradigm has been applied to database technology, creating a new programming model known as object databases. These databases attempt to bring the database world and the application programming world closer together, in particular by ensuring that the database uses the same type system as the application program. This aims to avoid the overhead (sometimes referred to as the impedance mismatch) of converting information between its representation in the database.

Database storage structures

Relational database tables/indexes are typically stored in memory or on hard disk in one of many forms, ordered/unordered flat files, ISAM, heaps, hash buckets or B+ trees.

Контрольные вопросы:

1. What is a database?

2. What are the famous database architectures in use?

3. What do you know about database management systems (DBMS)?

4. What is a Relational Database Management System (RDBMS)?