# Database Questions Pg.80

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Alex Swan Mr. Davis 9/18/12 Homework Review Questions 3.1 Define the following terms as they apply to the relational model of data: Domain – Set of atomic (indivisible) values. Attribute – it describes a component of the database, such as a table or a field. N-tuple – in mathematics, an ordered set of n elements called its components or coordinates. Relation Schema – It is representation of database highlighting relationships that we have created. Relation State – set of tuples that have the same attributes. Degree of a relation – number of attributes n of its relation schema. Relational Database Schema – Tables, columns and relationships that make up a relational database. Relational database state – is a union of…show more content…
Therefore, the super superkey is always the set of all attributes of a relation. 3.5 Why do we designate one of the candidate keys of a relation to be the primary key? - When there are more than one keys in a relation schema of database, all these keys are referred to as candidate keys. But, a particular candidate key is called as a primary key over the other candidate keys. This primary key is generally a single attribute or a smaller number of attributes. We designate so because it becomes fairly easier to deal with a database when we can have a single distinct key for a particular relation instead of having more than one key. 3.6 Discuss the characteristics of relations that make them different from ordinary tables and files? - Ordering of tuples in a Relation: The tuples are not considered to be ordered, even though they appear to be in the tabular form. - Ordering of attributes in a relation schema R and of values within each tuples: We consider the attributes in R(A1, A2, .., An) and the values in t=&lt;v1, v2, .., vn&gt; to be ordered. - Values in a tuple: All values are considered to be atomic or indivisible. A special null value is used to represent values that are unknown or inapplicable to certain tuples. 3.7 Discuss the various reasons that lead to the occurrence of NULL values in