Cornerstone of data design
Store data once
Data storage
- Data must be available when the user wants to use it
- Data must be accurate and consistent
- Efficient storage of data as well as efficient updating and retrieval
- Necessary that information retrieval is purposeful
Data storage approaches
- Store data in individual files
- Each unique to particular application - Store data in database
Define database
A formally defined and centrally controlled store of data intended for use in many different applications
Effectiveness objectives of the database
- Ensure that data can be shared among users for a variety of applications
- Maintaining data that is accurate and consistent
- Data required for current and future applications will be readily available
- Allow the database to evolve as the needs of the user grows
- Allow users to construct their personal view of the data without concern for the way that data is physically stored
Data vs Metadata
Data
- collected about people, objects, or events in reality and eventually stored in a file or database
Metadata
- information that describes data
Entities
- Any person, object or event about which someone chooses to collect data
- Can be a person, place or thing
- May be an event or unit of time
Entity consists of rows called
Records
A record consists of properties of the entity (–> attributes)
Specific record is an instance of the entity
Relationships
Used to link data entries
- one to one
- one to many
- one to many (mandatory on many side)
- one to many (optional on many side)
Key properties
- Uniquely identify records
- Are dataless
- Never null
- Never change
- Can be used in combination
File types
- Master file
- Table file
- Transaction file
- Report file
o Used when necessary to print report and no printer is available
o Useful as users can take files to other computer systems and output to
specialty devices
Master file
- Contain records for a group of entities
- Contain all information about a data entity
Table file
- Contain data used to calculate more data or performance measures
- Usually read-only by program
Report file
- Used when necessary to print report and no printer is available
- Useful as users can take files to other computer systems and output to specialty devices
Relational Databases
- Databases are intended to be shared by many users
- In relational data structures, data is stored in many tables
3 structures for storing database files
- Relational database structures
- Hierarchical database structures
- Network database structures
Optionalities
- Used to refine Entity- Relationship diagram
- Enforce specific business rules pertaining to the data
- Once optionalities are added, the diagram is called an Extended Entity-
Relationship Diagram (EERD)
