Tutorial:  How are Relational DBMS classified?

 

Relational DBMS is classified software in 4 levels:

Classification

Description of features

Fully relational

Supports all eight relational algebra functions and enforces both entity and referential integrity rules.

Relational complete

Supports all relational algebra functions but does not support integrity rule.

Minimally relational

Supports only SELECT, PPROJECT and JOIN.

Tabular

 

Supports only SELECT, PPROJECT and JOIN and requires that all access paths be defined by the user.

 

??? What are eight relational algebra functions?

       Eight relational algebra functions are SELECT, PROLECT, JOIN, INTERSECT, UNION, DIFFERENCE, PRODUCT, and DIVIDE. (More detail see Appendix 1)

??? So, What are entity and referential integrity rules?

              Entity integrity rules means the table’s primary key column has no null entries.

               Referential integrity rules means A table contains a foreign key which links entries in the A table to the other table(B table). For example:

               A table

CUS_NUM

CUS_NAME

CUS_ADD

REP_NUM

20033

William

124,New St.

25

20034

Real

35, Old St

26

20035

GQ

TT St #2

20036

TT

GG St #3

69

 

Entity integrity:

no null values in this column.                                     Referential integrity: matching 

                                                                                    values in other table or null values. 

          

                                                                 match

                                                                 match                                                                                          

                                                   B table

REP_NUM

SALE

25

TV

26

DVD

55

Radio

 

 

??? How do you classify ORACLE and XDB software?

More information about relational database classification:

  1. Software such as ORACLE, XDB and Ingress approach the fully relational status.
  2. Microcomputer software packages such as Ashton-Tate’s original dBASE II and the follow-up dBASE III are best described as tabular.
  3. Minicomputer relational database software is usually minimally relational.
  4. Finally, before you buy software labeled “relational”, you may find it useful to ask some specific questions, using the relational database classification table to find out the extent of the relational support provided by the software.

 

Summary:

 

 

 

Some questions below will help us to review and memorize the concept of relational database classification.

 

Multiple choices

 

1. A relational system such as SQL that supports all eight table operations of the relational algebra is said to be:

a. Fully relational                                                                       b. Table relational      

c. Minimally relational                                                   d. Relationally complete

 

Ans: D

 

2. A system that supports all aspects of the relational model, including domains and two basic integrity rules is said to be:

a. Fully relational                                                                       b. Table relational      

c. Minimally relational                                                   d. Relationally complete

 

Ans: A

 

Short questions

 

1. What is the purpose of classifying relational DBMS?

Ans: Classifying relational DBMS can grade database software and helps us implement a database design easily.

 

2. In relational DBMS classification, gave the differences between

1)      Fully relational and relationally complete.

2)      2) Minimally relational and tabular.

 

Ans 1: Fully relational supports all relational algebra functions and enforces both entity and referential integrity rules.

Relationally complete supports all relational algebra functions but does not support integrity rules.

Ans 2: Minimally relational supports only SELECT, PPROJECT and JOIN.

Tabular supports only SELECT, PPROJECT and JOIN as well as user must define all access paths.

 

References:

1.  http://www.cs.appstate.edu/~rt/DBMS/notes/chap1.pdf

2. http://www.frick-cpa.com/ss7/Theory_RelationalDB.asp

3. Mittra, Sitansu S. Principles of Relational Databasde Systems. Englewood Cliffs, NJ: Prentice Hall, 1991.

4. Peter Rob, Carlos Coronel. Database Systems: Design, Implementation, and Management. Wadsworth Publishing Company, CA, 1995.

 

Appendix 1

The Relational Algebra

SELECT: Create a new table containing rows of original table satisfying certain criteria.

PROJECT: Create a new table by deleting certain columns from original table.

PRODUCT: Form new table by concatenating each row in first table with each row in second.

UNION: Form new table containing all rows of both input tables (tables must match on all attributes).

DIFFERENCE: Form new table containing all rows in first table but not in second (tables must match on all attributes).

JOIN: Form new table by combining records from two tables that match on a common attribute.

INTERSECTION: Form new table containing all entries appearing in both input tables (tables must match on all attributes).

DIVIDE: The concept of division is related to that of the A product in that R X S divided by S yields R. Divide therefore is essentially an inverse of A product in the same way as arithmetic divide is the inverse of multiplication.

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