Topic 141

Global databases by Ken

The term or expression database originated within the computer industry. A database is a structured collection of records or data which is stored in a computer so that a program can consult it to answer questions. The records retrieved in answer to the questions become information that can be used to make decisions. There are a number of different ways of organizing a schema, that is, of modelling the database structure: these are known as database models. A schema is a structural description of the type of facts that are held in the database. There are many different kinds of data base models.

The flat model consists of a single, two-dimensional array of data elements, where all members of a given column have similar values, and all members of a row are related. For instance, names and passwords might use a flat model. Each row would have the specific password associated with an individual user. The columns of the table have a type associated with them, for example character data, date or time information, integers, or floating point numbers. It is basically like a spread sheet.

A hierarchical model organizes data into a tree-like structure. It implies a single upward link in each record to describe the nesting. It also implies a sort field to keep the records in a particular order in each same-level list. These were widely used in the early mainframe database management systems, like the Information Management System. It now describes the structure of XML documents. This model is very efficient to describe many relationships in the real world, like recipes, table of contents, ordering of paragraphs, or any sorted information.
The network model organizes data using two fundamental constructs, called records and sets. Records contain fields and sets define one-to-many relationships between records. A record may be an owner in any number of sets, and a member in any number of sets.

The operations of the network model can be navigated. A program navigates from one record to another by following the relationships in which the record participates. Records can also be located by supplying key values.

Although it is not an essential feature of the model, network databases generally show the set relationships by means of pointers. They directly address the location of a record on a disk. This gives excellent retrieval performance.

A relational model is a mathematical model defined in terms of predicate logic and set theory. Three key terms are used extensively in relational database models: relations, attributes, and domains. A relation is a table with columns and rows. The named columns of the relation are called attributes, and the domain is the set of values the attributes are allowed to take. The basic data structure of the relational model is the table, where information is represented in columns and rows. Thus, the "relation" in "relational database" refers to the various tables in the database.

The columns enumerate the various data, and a row is an actual instance of the data that is represented by the relation. As a result each table shows different kinds of information that can be related. This database is used the most in the global society.

Databases are preferred for the storage of large multiuser applications, where coordination between many users is needed. Even individual users find them convenient, and many electronic mail programs and personal organizers are based on standard database technology. Advanced databases will help the global society store and retrieve information. This will help communication, which will make every society more involved or dependent on each other.