¶ … Coding relational algebra operations varies from school to school. I wrote it according to my training, but there are variations. Review and rewrite in own words so as to preclude plagiarism.
What is a relation schema? What is the difference between a relation, a relation schema, and a relational schema?
A relation schema is the basic information that describes a table or a relation. This includes the set of column names, the data within the columns, or the name associated with the entire table.
For example 'Students' would be the relation (I..e category) name.
The relation schema for students may be expressed as following:
Students (sid: string, name: string, login: string, age: integer, gpa: real)
It has five fields or columns each having names or types.
The relation, in other words, is the topic / category (e..g 'student'), the relations schema is the property categories of the relation, or of the 'student' table.
A relational schema refer to the meta-data elements which are used to describe the way that the Table is laid out. It describes the lay out and the constraints of the data in that particular SQL domain, or, in other words, it is a logical description of the design of the database. For instance, if a relation account would possess the categories of account_number, branch_name and balance, the algorithm of the relational schema would be thusly:
Account_schema= (account_number, branch_name, balance)
The primary key is the tag in the relational table...
The primary key can refer to either unique data such as a person's social security number or it can be globally unique data.
Primary keys can consist of a single unique attribute or they can be a combination of attributes.
As an example, we have the relational scheme of the Table that has each student's name. The ID number is a good choice for a primary key since it is unique. Their first and last name would not be a good choice as primary key since these can always be duplicated. There can be only one primary key in a database and this is the difference between a primary key and a candidate key.
The candidate key refers to any column or combination of columns that can serve as the unique key in the database. Candidate names also do not have extraneous information in them. SSN, for instance, can be a candidate name. Unlike the primary key, there can be many candidate keys in one table . Primary keys are also seldom changed as well as being non-Null.(SQL Authority)
3. 1. Define and Identify the superkeys, candidate key(s), and the primary key for the following relation instance of the STU-CLASS relation schema.
Student Number; Student name; Student major; Class Name; and Class Time are super keys.
Candidate keys are Student Number and Class Name. The Primary Keys are Student number, and possibly -- only if not replicated in the future, Class Name.
1. Define the term referential integrity constraint. Why is referential integrity important? How is…
