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.