Data Management, Databases and Information Systems
Data Management, Databases and Information Systems examines how raw data becomes useful information and how databases keep that information consistent. Expect questions on keys, relational structure, validation, queries and the difference between a database and a DBMS.
From data to information
- Data is raw symbols; information is processed data with meaning and context. Good information is accurate, timely, relevant and complete.
- A flat-file system stores one table and often repeats data, causing redundancy and inconsistency. A relational database splits data into related tables to reduce duplication.
Structure and integrity
- A table contains records, which are rows, and fields, which are columns. A primary key uniquely identifies each record and cannot be null. A foreign key refers to a primary key in another table and enforces referential integrity.
- Data types such as text, number, date and Boolean constrain what can be stored. Validation checks data on entry using rules such as range, type, presence and format; verification checks that data was copied or entered correctly, for example by double entry.
- A DBMS is software that manages the database: storage, concurrent access, security, backup and querying. SQL is used to define and manipulate data.
Worked example
A school has Student(StudentID, Name, DateOfBirth) and Enrolment(StudentID, CourseID, Grade). StudentID is the primary key of Student. In Enrolment, StudentID is a foreign key linking each enrolment to one student. The primary key of Enrolment is the composite (StudentID, CourseID), because a student takes several courses and a course has several students.
Traps
Do not call a foreign key unique in its own table. Validation does not prove accuracy: a valid date can still be the wrong date. Do not confuse sorting, which orders records, with querying, which selects records.