Information Systems & Databases 2.2) Organisation methods

A database is an organised collection of data. Non-computerised databases include: telephone book address book recipe cards

Advantages of non-computerised databases: no power required no training required inexpensive data not a linked security risk Advantages of computerised databases: easily edited large storage fast retrieval display options

A flat file database organises data into a single table. Flat file databases organise the data into: files – a block of data; divided into records and fields record – a collection of facts about one specific entry field – a specific category of data in a database character – smallest unit of data (e.g. letters, numbers, symbols)

Keys are fields that are used to sort and retrieve information. Keys include: single key – derived from one field composite key – made by joining two or more keys together primary key – a field that has a set of unique values secondary key – a field that does not contain unique data

A relational database organises data into a series of linked (related) tables. The organisation of data in a relational database involves a schema. A schema is the data definition for a relational database. It shows the entities, relationships and attributes.

An entity is the specific thing about which the data has been collected. E.g. in school – student contact details, merits/demerits, reports, attendance. Each table is one entity. An attribute is a defined property of an entity. Attributes are the same as fields in flat file databases.

A relationship is the way in which entities are related to each other. Entities are related through primary keys. Entities can be related in one of three ways: one to one one to many many to many

Data modelling is the process of identifying entities, their attributes and the relationships between those entities through certain attributes. Some tools that are used include: data dictionaries schematic diagrams normalisation Data dictionaries are comprehensive descriptions of each attribute.

Each data dictionary contains metadata such as: field name – should be short, clear and unambiguous data type – kind of data (text, number, date, time, logical (Boolean)) field size – number of characters allowed in an attribute description – specifies the contents of an attribute

The data dictionary is the basis for database creation. If there are multiple designers it allows them to see if a particular attribute already exists in another entity. This can help to eliminate data redundancy, which is the undesirable duplication of data within a database. [p.52 – Complete learning activity 4, parts (a) & (b) ]

Schematic diagrams are graphical tools that help define the database and describe a schema. An entity-relationship diagram (ERD) is a graphical method of identifying the entities and their attributes and showing the relationships between entities. [Draw Diagram 2.13, p.48]

Hypermedia is a combination of media whose locations are linked electronically. The information is stored using a set of documents that may contain: text images video audio animations executable files

Information is retrieved using hypertext. Hypertext is the system that allows documents to be cross- linked in such a way. A link, or hyperlink, is usually indicated by a highlighted item.