Unit 5 - Relational database concepts

Unit 5 - Relational database concepts

1. A. Describe the terms typically used in relational database terminology

   • TABLE - Contains data about 'things' and is made up of records
   • RECORDS - A single row within a table. It is a collection of data
   • FIELD - An individual data item within a record
   • PRIMARY KEY - A field that allows each record to be uniquely identified
   • FOREIGN KEY - Used to link tables together through a primary key
   • RELATIONSHIPS
     • One to One
       • One record in one table can only be linked to one record in another table
     • One to Many
       • Many records in one table can be linked to many records in another table
     • Many to Many
       • Many records in one table can be linked to many records in another table
   • ENTITY - The name given to anything you can store data about. E.g. CUSTOMER, SUPPLIER
   • ATTRIBUTE - A characteristic of an entity E.g. for CUSTOMER would be 'Surname'

2. B. Data dictionary

   • The table below shows the basic data that would be expected in all data dictionaries

3. C. Data Tyoes

   • BOOLEAN
     • Boolean data holds one of two values, for example:yes/no, true/false
   • REAL
     • A 'Real' data type is numerical data which contains decimal numbers.
       • It would be used when extra detail is required and a whole number would not provide enough information.
   • iNTEGER
     • An Integer data type stores whole numbers. The numbers can be both positive or negative but they cannot contain decimal points or fractions.
   • TEXT/STRING
     • A text or string data type can hold any alphanumeric character including text, numbers and symbols. The data can be pure text or a combination of text, numbers and symbols.
   • DATE/TIME
     • A date / time data type is used to store any data that is related to date or time.

4. D. Queries

   • PARAMETER QUERIES - 'A parameter is the value that is used by the query to select the records.'
   • STATIC
     • When you set up a query, if you put in a specific search criteria that you are looking for, for example in the query below, 'chapman' has been entered as the parameter (search criteria) for LastName.
       • The parameter (chapman) has been hard coded into the query. This means that everytime the query is run, it will only ever search for records which contain the last name of Chapman.
         • This is called a Static Parameter Query.
   • DYNAMIC
     • Because the type of query before would be used a lot, it wouldn't really be the best way of setting up a query to search for a customer by their last name. It would mean opening the query every time and manually changing the parameter before running the query.
       • Instead, a 'dynamic parameter query' would be a better way of setting up such a query.

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