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.