Information Systems & Databases

1. Information Systems & Databases 2.2) Organisation methods

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

3. 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

4. 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)

5. 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

6. 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.

7. 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.

8. 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

9. 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.

10. 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

11. 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) ]

12. 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]

13. Hypermediais 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

14. 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.