The Characteristics of Databases

• The purpose of a database is to keep track of things.
• Relational Databases are the most common form of database today.
  • Built in units of a table
  • In the book, they will name tables in all upper case
    • CLASS, GRADE, STUDENT
    • This is a convention, not a syntax requirement.
  • Each table has a number of rows
  • The rows represent an instance of a thing.
  • Think of rows as a record in C++
  • Each row has a number of columns
  • In the book they will name columns in MixedCase
    • StudentNumber, EmailAddress, ...
    • Again, a convention, not a syntax requirement
  • Think of a column within a row as a field within a record in C++
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  • These two tables are part of a database, but there is not inter-relationship between them.
  • Adding a third table:
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  • This table provides a linking between students, classes and grades.
    • The StudentNumber in the GRADE table provides a reference to the student in the STUDENT table.
    • The same is true with ClassNumber
  • Each row in a table is uniquely identified by a primary key
  • In the above tables, StudentNumber is the primary key in the STUDENT table.
  • If we know the student number, then we know the key.
  • The same is true of ClassNumber and the CLASS table.
  • For this database, the DBMS generates the student number for us.
  • This is known as a surrogate key
  • For the GRADE table, the primary key consists of two parts.
    • The StudentNumber from the STUDENT table
    • The ClassNumber from the CLASS table.
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    • Since the data is from another table, this is called a foreign key
    • Adding a foreign key creates a relationship between tables.
    • Perhaps another view
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  • We will spend quite a bit of time discussing keys, tables, relations, and other topics.
• The author claims that databases create information
  • Data is defined as recorded facts and numbers.
  • Information is
    • Knowledge derived from data
    • Data presented in a meaningful context
    • Data processed by summing, ordering, averaging, grouping, comparing, or other similar operations.
  • Databases are used to organize data so that information can be produced.
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