August 05, 2006

The relational database model represented a landmark in the history of database modelling, as it allowed files to be related to each other by means of a common field. In order to relate any two files, they simply need to have a common field, which makes the model extremely flexible.

Formally introduced by Dr E.F. Codd in 1970, the relational model provides a simple, yet rigorously defined, concept of how users perceive data. The relational model represents data in the form of two-dimension tables. Each table represents some real-world person, place, thing, or event about which information is collated. A relational database is a collection of two-dimensional tables.

A basic understanding of the relational model is necessary to effectively use relational database software such as Oracle, Microsoft SQL Server, or even personal database systems such as Access or Fox, which are based on the relational model.

Relational tables have six properties:

1. Values are atomic.
2. Column values are of the same kind.
3. Each row is unique.
4. The sequence of columns is insignificant.
5. The sequence of rows is insignificant.
6. Each column must have a unique name.

A relationship is an association between two or more tables. Relationships are expressed in the data values of the primary and foreign keys. A primary key is a column or columns in a table whose values uniquely identify each row in a table.

A foreign key is a column or columns whose values are the same as the primary key of another table. You can think of a foreign key as a copy of primary key from another relational table.

Keys are fundamental to the concept of relational databases because they enable tables in the database to be related with each other. Navigation around a relational database depends on the ability of the primary key to unambiguously identify specific rows of a table.

Data integrity

This means, in part, that you can correctly and consistently navigate and manipulate the tables in the database. There are two basic rules to ensure data integrity: entity integrity, and; referential integrity.

The entity integrity rule states that the value of the primary key can never be a null value (a null value is one that has no value and is not the same as a blank).

The referential integrity rule states that if a relational table has a foreign key, then every value of the foreign key must either be null or match the values in the relational table in which that foreign key is a primary key.

Data manipulation

Relational tables are sets. The rows of the tables can be considered as elements of the set. Operations that can be performed on sets can be done on relational tables.

The eight relational operations are:

— Union;
— Difference;
— Intersection;
— Product;
— Projection;
— Selection;
— Join, and;
— Division.

Normalisation is a design technique that is widely used as a guide in designing relational databases. Normalisation is essentially a two step process which puts data into tabular form by removing repeating groups and then removes duplicated data from the relational tables.

After having a basic understanding of relational database modelling, let’s have a look at some of the applications that are designed using relational database modelling concepts.

Oracle Database 10g Express Edition: This is a no-frills edition of the proven Oracle Database product. It can be installed on any machine, supports up to 4GB of user data, runs on a single processor and uses a maximum of 1GB memory.

Main features
— Available for 32-bit Linux and Windows;
— May be installed on a multiple CPU server, but only executes on one processor in any server;
— May be installed on a server with any amount of memory, but will only use up to 1GB RAM of memory.

FACTbroker: FACTbroker’s data-centric approach powered by the XML driven framework has lent the product to position itself in the forefront in the arena of business intelligence reporting.

Main features
— Reliance on existing RDBMS knowledge;
— Seamless integration with existing security infrastructure;
— Authorisation driven user interface, and;
— Intuitive, yet powerful Control Centre for XML configuration.

Kdb database platform: Kdb is a high-performance relational database platform for 32-bit architectures.

Main features
— Relational database optimised for fast search;
— Unlimited data capacity at main-memory speeds;
— Time series analysis built in;
— Billions of records analysed in seconds, and;
— 32-bit architecture runs on Solaris, Linux and Windows.

NRG Global DbVisualiser: This is a cross-platform database tool for all major relational databases. DbVisualiser enables simultaneous connections to many different databases through JDBC drivers.

Main features
— Browse database structure;
— View detailed characteristics of database objects;
— Edit table data graphically;
— Execute arbitrary SQL statements or SQL scripts, and;
— Reverse engineer primary/foreign key mappings graphically

PointBase Embedded: This is a full-featured and zero administration Java relational database that enables software vendors to accelerate development cycles and reduce time to market.

Main features
— Delivers cross-platform portability, a small footprint and comprehensive security;
— Offers a low-cost, high results solution to effective storage of metadata, application-specific data or out-of-box tutorials and demonstration materials, and;
— It can be integrated directly within your application making it completely transparent to the end-user.

Pervasive Postgres: This is a validated and supported distribution of PostgreSQL, the world’s most advanced open source database.

Main features
— Offers support, updates, and value added tools in a subscription model, as well as professional services for migration and training, and;
— Pervasive’s backing, support and services provide the assurance that enterprises need to confidently put open source to work.

VistaDB: This is an alternative to Microsoft Jet/Access, MSDE, and Xbase for building robust small to midsize .NET database applications.

Main features
— First real alternative for professional programmers that rely on the Microsoft Jet engine and Access databases to store and manage data, and;
— VistaDB is a true RDBMS specifically designed for .NET to give developers a robust, high-speed embedded database solution with minimal overhead.

Solid FlowEngine: This uniquely combines two enabling technologies:

— Relational data management, and;
— Advanced, bi-directional multi-point synchronisation.

It fuses these two elements into an embeddable distributed data management platform, the Solid FlowEngine. Solid FlowEngine provides an underlying foundation for high performance distributed applications built to meet stringent carrier-grade requirements.

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