As we begin examining database concepts, we need to be certain we are familiar with certain terms - data versus information. Data refers to facts concerning objects and events that could be recorded and stored on computer media. Information is data that have been proceeded in such a way that the knowledge of the person using the data is increased. Another term to become familiar with is metadata - this is data that describes the properties or characteristics of end-user data and the context of that data.
As described in the introduction, database organizations (models) evolved after the flat file model. File processing systems encompassed the flat file group of data files. Flat files had several disadvantages - such as dependence between flat files and programs, duplication of data, limited data sharing between programs, lengthy development times, and excessive program maintenance whenever a file was changed.
When database models came into use, the database models emphasized integration and sharing of data and included advantages of program-data independence, planned data redundancy (limited redundancy), improved data consistency, improved data sharing, increased productivity of application development, improved data quality, improved data accessibility and responsiveness, reduced program maintenance, and improved decision making. Some of the costs and risks include: new specialized personnel, installation and management cost and complexity, conversion costs, the need for explicit backup and recovery and organizational conflict with ownership of data.
The software system that controls the data base is DBMS - database management system. A database management system is a software system that is used to create, maintain, and provide controlled access to user databases - in other words it creates, updates, stores and retrieves data from the database.
Databases have been subdivided into how they are used - Personal databases, workgroup databases, departmental/divisional databases, enterprise-wide databases, and web-enabled databases.
As mentioned in the introduction - database models evolved after the flat files. Database models began in the late 1960's with the hierarchy model that was begun primarily through IBM. This model uses the tree structure for data storage. This model still exists today, but is primarily legacy systems.
In the 1970's the Network model came into being through a consortium of companies. The model uses the linked list as the structure for data storage. This model did not gain popularity and did not last long.
In the 1980's the Relational model was created. This model uses a 2-dimentional table as the structure for data storage. This model is still the number one database model in use today.
In the 1990's the object-oriented model was created. This model uses the object as the structure for data storage.
Also in the 1990's the object-relational model was created. This model is actually a relational database model in reality, but has an object-oriented front end for user interface.
Data warehousing came into being in the 1990's as well. This is a method for extracting database "data" - cleaning that data (making it consistent and correct), and restoring the data into "warehouses" for use with data mining products.
Web-endabled databases started in the late 1990's where traditional relational databases were combined with web-programs to support such things as e-commerce, customer management and service areas.