IST210 STUDY - Study Sheet Synonyms Table File Relation Row...

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Study Sheet Synonyms Table – File – Relation Row – Record – Tuple Column – Field – Attribute o A key is one (or more) columns of a relation that is (are) used to identify a row o A composite key is a key that contains two or more attributes For a key to be unique, often it must become a composite key Ex : The composite key is: (FirstName, LastName, DOB) o A candidate key is called “candidate” because it is a candidate to become the primary key A candidate key is a unique key Exs: Penn State ID SSN Access ID (FirstName, LastName, DOB) o A primary key is a candidate key chosen to be the main key for the relation If you know the value of the primary key, you will be able to uniquely identify a single row o A Surrogate Key is a unique, numeric value that is added to a relation to server as the Primary Key Surrogate Key values have no meaning to users and are usually hidden of forms, queries and reports A Surrogate Key is often used in place of a composite primary key o To preserve relationships, you may need to create a foreign key A foreign key is a primary key from one table placed into another table The key is called a foreign key in the table that received the key Ex: Table1: Employee: EmployeeID(Surr. Key), Name, Phone Number, DepartmentID(For. Key) Table2: Department: DepartmentID(Surr. Key), Name o Referential integrity states that every value of a foreign key must match a value of an existing primary key Must be the same data type The primary key value must exist before the foreign key value is entered o Functional Dependency o A relationship between attributes in which one attribute (or group of attributes) determines the value of another attribute in the same table Ex: The price of one cookie can determine the price of a box of 12 cookies: (cookiePrice, Qty) -> BoxPrice
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o By definition… A candidate key of a relation will functionally determine all other attributes in the row o Likewise, by definition…
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  • Spring '08
  • MCCONN,CHARLOTTERYOO,JUNGWOO

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