Coding Relational Algebra Operations Varies From School

¶ … 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 that gives each record in the table its own identifier. 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 the term foreign key used in the context of referential integrity? Referential integrity is the constraint n a database that ascertains that references between data are valid and intact. Its purpose serves to ensure that a database should not only store data but should also seek to ensure its quality. As way of ensuring referential integrity, every foreign key is matched with a primary key.

For example student SSN in the school's main record (for instance) may be matched with that particular student's class in an another record. When the primary key (SSN) is deleted, the class number (foreign key -- connected to primary key) is simultaneously deleted too. Referential integrity has many important benefits. Some of these include the following: 1. Improved data quality. There may still be errors but data is more authentic and correct. 2. Faster development 3. Fewer bugs -- declarations of referential integrity are more concise than the equivalent programming code. 4.

Consistency across applications -- referential integrity ensures that the quality of data references across the multiple applications are consistent and accurate (Blaha, pdf) DRIVER (Dr_license_no, Dr_name, Dr_city, Dr_state) TICKET_TYPE (Ttp_offense, Ttp_fine) TICKET (Tic_ticket_no, Tic_ticket_date, Tic_dr_license, Tic_ttp_offense) An instance of each of these relations follows. Use the data shown below to (a) write the answer to each question and (b) define and list the relational algebra operation(s) required to obtain the answer. a.

What are the names of all drivers? Dr_Name = (Mills. Brooks. Silva. Lance. Blair .newman). This is a conjunciton relational algebra operation indicating a group of indivdiuals belonging to one category. a. What are the license numbers of all drivers who have been issued a ticket?