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Relational Databases
| Question | Answer |
|---|---|
| What are the three models of database system that have dominated over the history of database management systems? | a. hierarchical Model b.relational model c.network models |
| What is the relational term for a row of related data values? | tuple |
| How are the table name and the column names used in database study? | row attribute |
| What is the relational term for a column in a row of records? | attribute |
| What is the relational term for a collection of records about some object? | relation name |
| How is the primary key denoted in a relation diagram? | underlined |
| What is the term for a set of values each of the same data type in which each value is indivisible? | domain |
| What term is used to refer to a value that is indivisible? | atomic |
| What is the term that refers to the structure of a value? | data type |
| What is the term for the description of a relation? | schema |
| What is the relational term for a role or characteristic of a data element in a tuple of a relation? | |
| Using common database notation, denote a relation, Part, that has attributes partno, name, cost and qoh. | Part(part no,name,cost,qoh) |
| What is the term that refers to the number of attributes in a relation schema? | degree |
| What is the term that refers to a relation and all of its tuples at an instant in time? | Relation State |
| Does a relation in relational database theory have an order? | False |
| A domain, months, has a possible range of 12 values, January, February, March, etc. What is the term for the number of values in a domain? | cardinality |
| What is the term for the state of a relation that meets all constraints as defined in the relation schema? | Valid State |
| In a database attribute, a value that is unknown, exists but is not available, or is a value that is undefined is said to be __________. | null |
| If a relation, CUSTOMER, and a relation, VENDOR, both have a primary key, id, how would a user reference the two with dot notation in a query that uses both? | customer.id vendor.id |
| What is the term that refers to restrictions on the actual values in a database state? | Constraints |
| What kind of constraint can be expressed in a schema of a data model? | explicit |
| What kind of constraint is just part of the relational data model? | implicit |
| What is the term for constraints that cannot be directly expressed in schemas and must be expressed and enforced by an application program? | Business Rules |
| List five of the domain constraints that we studied | a. Booleans b. Characters c. time d. money e. fixed length strings |
| What is the term for any combination of attributes that can be uniquely used to identify a database record? | Superkey |
| What is the term for a superkey from which one cannot remove any attributes and still have the uniqueness constraint? | Key |
| A relation can have more than one key, so what is the term for another one of those keys? | Candidate Key |
| What is the term for a candidate key that is used to identify a relation? | primary key |
| What is the term for a candidate key that is NOT used to identify a relation? | foreign key |
| What displaying the structure of a relation, how is the primary key identified? | Underlined |
| What does the entity integrity constraint specify? | No primary key can be null |
| What is the key constraint? | Uniqueness |
| What is the term for a constraint that is specified between two relations in order to maintain consistency between the two relations? | referential integrity constraint |
| What are the two requirement specified for a foreign key? | a.Attributes in foreign key have same domain as primary key attributes Not yet graded b. Value of foreign key in a tuple of the current state either occur as a value of primary key or be null |
| What do you call constraints that may be specified by application programs or some general purpose constraint definition language rather than the data definition language? | semantic integrity constraints |
| What constraint states that the value of one attribute determines the value of a different attribute? | functional dependency constraint |
| What are the three operations that change the state of a relation? | a. insert b. delete c. update |
| How could an INSERT operation on a relation cause a violation of the key constraint? | if a key value in the new tuple already exists in another tuple relation. |
| How could an INSERT operation on a relation cause a violation of the entity integrity constraint? | if any part of the primary key of a new tuple is null |
| How could an INSERT operation on a relation cause a violation of the referential integrity constraint? | if value of foreign key in the new tuple refers to a tuple that doe not exist in the referenced relation. |
| What is the default action caused by a violation of any constraint of the relational database? | reject |
| How could a DELETE operation on a relation cause a violation of the key constraint? | does not violate key constraint |
| How could a DELETE operation on a relation cause a violation of the entity integrity constraint? | does not violate entity integrity |
| An alternative to rejecting a DELETE operation that removes a tuple with a primary key that is being referenced by another tuple’s foreign key is to CASCADE. What occurs with a CASCADE action? | delete all referring tuples |
| What is another alternative to REJECT and CASCADE, when a DELETE operation removes a tuple with a primary key that is being referenced by another tuple’s foreign key? | set to null |
| What is the term for an executing program that includes one or more database operations? | transaction |
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