Chapter 5

Chapter 5

1. key terminology

   • table
     • - The table must have unique name
     • - Each field/column must have a unique name
     • - Each record/row must be unique
     • - Each data item within a field must contain only a single data item
   • Record
     • A record is a single row within a table. It is a collection of data about a single item or a single event e.g. a record might be about an individual,
       • such as customer or an order being placed
     • Records are made up of fields and can contain different data types. In each table each record must be unique
   • Field
     • Records are made up of fields and can contain different data types. In each table each record must be unique
     • Records are made up of fields and can contain different data types. In each table each record must be unique
     • Records are made up of fields and can contain different data types. In each table each record must be unique
   • Key
     • Primary key
       • The primary key is a field in a table that allows each record to be uniquely identified. Every value of the primary key must be unique.
     • Secondary Key
       • • A secondary key is a field that is identified as being suitable for indexing the data
       • • It is used to sort the data in a different order to the primary key
       • • It is used to sort the data in a different order to the primary key
     • Foreign key
       • • Is used to link tables together. A foreign key is a field in one table and is linked to a primary key in another table
       • • The data types of the fields that are linked must linked must be the same

2. Relationships between entities

   • Entity is also defined as a table
   • • Entities can be classified into entity types
   • • Exact definition An Entity is a person, place, thing or concept about which data can be collected. Examples include EMPLOYEE, HOUSE, CAR
   • You get one to many, one to one and many to many relationships

3. Entity and Attribute

   • An entity is a name for a logical or physical storage unit

4. Normalisation

   • Normalisation is a process applied to data structures to decrease redundancy and to increase its integrity.
   • 1NF
     • every data value is atomic
     • no repeating data
     • primary key (each row must be uniquely identifiable)
   • 2NF
     • - non-key attributes are dependent on the entire primary key (no partial key dependencies)
   • 3NF
     • - no functional dependency between non-key item

5. Data dictionary

   • table name, field name, data type, length, validation, relationships, security

6. Query

   • A simple query is one where there is only one parameter being searched
   • A complex query is one where there is more than one parameter
   • Static parameter query
     • one whose parameters are hard coded into the query and cannot be changed by the end user
   • Dynamic query
     • a dynamic query is one whose parameters are set by the end user at run time, usually by a dialogue box