12 ipt 0202 organisation methods
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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.
• One application of hypermedia is the World Wide Web.
• Each document is accessed through its uniform resource locator.
• A URL is the address of a file or resource on the Web.
• It links to an Internet Protocol (IP) number and is unique.
• The URL consists of three parts:• protocol (http, https, ftp)• domain name – address of a
specific computer where the website is hosted
• file path – links to a specific page or resource.
• URL’s must be exact and complete or they will not work.
• A storyboard is a series of frames, each representing a different action or image.
• It is a tool used by hypermedia.• They consist of navigation paths,
information and graphics.• They are popular because they are
easy to read and modify.
• Four main storyboard layouts are:• linear – simple sequential path• hierarchical – branching top-down design
• non-linear – no structure• combination – a blending of the above
• Web pages are created using hypertext markup language (HTML).
• HTML is a set of special instructions that describe how the parts of a document are displayed.
• They are actually text files with special HTML instructions.
• An HTML editor is a program that specialises in writing HTML code.
• Instructions are given using HTML tags.
• These tags are metadata because they are information about the data.
• Links are achieved though text or images using specialised HTML tags.
• Tags are usually paired to start and end an instruction.
• E.g. <B> and </B> will make all text between them bold.