1 / 14

Database Design

Database Design. Dr. M.E. Fayad, Professor Computer Engineering Department, Room #283I College of Engineering San José State University One Washington Square San José, CA 95192-0180 http://www.engr.sjsu.edu/~fayad. Lesson 08-2: Misc. Topics in DB. 2. Lesson Objectives.

ursula
Download Presentation

Database Design

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Database Design Dr. M.E. Fayad, Professor Computer Engineering Department, Room #283I College of Engineering San José State University One Washington Square San José, CA 95192-0180 http://www.engr.sjsu.edu/~fayad SJSU -- CmpE

  2. Lesson 08-2: Misc. Topics in DB 2 SJSU – CmpE --- M.E. Fayad

  3. Lesson Objectives • Understand DB Terminology • Explain Relation Properties • Understand how to Identify Candidate, Primary, Alternate, and Foreign Keys • Understand Entity Integrity and Referential Integrity 3 SJSU – CmpE --- M.E. Fayad

  4. External Level View Level -- Users’ views of the db. Conceptual Level Logical View & Constraints View Internal Level Physical View or Computer’s view of the db. Terminology: ANSI-SPARC Database Architecture 4 SJSU – CmpE --- M.E. Fayad

  5. A Relation is a table with columns & Rows. An attribute is a named column of a relation. A domain is the set of allowable values for one or more attributes. A tuple is a row of a relation. The degree of a relation is the number of attributes it contains. More Terminology 5 SJSU – CmpE --- M.E. Fayad

  6. branchNo street city postCode B005 22 Deer Rd London SW1 4EH B007 22 Post St Aberdeen AB2 3SU B003 22 S. Main St Glasgow GI1 9QX B004 22 Mo Ave Bristol BS9 1NX B002 56 Clover Dr London NW5 6EU staffNo branchNo B005 B007 B003 B004 B005 Branch Example Staff Primary Key Foreign Key 6 SJSU – CmpE --- M.E. Fayad

  7. A Relation Schema – A named relation defined by a set of attribute and domain name pairs where: R (A1:d1, A2:d2, …., An:dn) A Database Schema – A set of relation schema each with a distinct name. R = (R1, R2, ….., Rn) More Terminology 7 SJSU – CmpE --- M.E. Fayad

  8. A relation has a name that is distinct from all other relation names within the same db. Each cell of the relation contains exactly one atomic (single) value. Each attribute has a distinct name. The values of an attribute are all from the same domain. Properties of Relations (1) 8 SJSU – CmpE --- M.E. Fayad

  9. Each tuple is distinct, there are no duplicate tuples. The order of attributes has no significance. The order of tuples has no significance, Properties of Relations (2) 9 SJSU – CmpE --- M.E. Fayad

  10. Superkey – An attribute, or set of attributes, that uniquely identifies a tuple within a relation. Candidate key – A Superkey, such that no proper subset is superkey within the relation. A candidate key, k, for a relation R has two properties: Uniqueness: In each tuple of R, the value of k uniquely identify the tuple. Irreducibility – no proper subset of k has the uniqueness property Relational Keys (1) 10 SJSU – CmpE --- M.E. Fayad

  11. They may be several candidate keys for a relation. Composite key – A key consists of more than one attribute. Exampes: Do you think “city” in Branch relation is a candidate key? The answer is no. Why? Because London has two branch offices, therefore, the attribute “city” cannot be a candidate key. Is “branchNo” a candidate key? Yes, Why? By Examining “branchNo”, each branch office has a unique branchNo, Is postcode is a candidate key? Yes.. Why? Relational Keys (2) 11 SJSU – CmpE --- M.E. Fayad

  12. Primary key: The candidate key that is selected to identify tuples uniquely within the relation Alternate keys – The Candidate keys that are not selected to be the primary key. Exampes: In the Branch Relation, we can choose branchNo as the primary key and Postcode as an alternate key. Relational Keys (3) 12 SJSU – CmpE --- M.E. Fayad

  13. Foreign key: An attribute, or a set of attributes, with one relation that matches the candidate key of some (possibly the same) relation. branchNo appeared in two relations: Branch and Saff relations branchNo is a primary key in Branch relation and it is a foreign key in the Staff relation. Relational Keys (4) 13 SJSU – CmpE --- M.E. Fayad

  14. T/F Each cell of the relation contains exactly on atomic (single) value. Primary key is the candidate key that is selected to identify tuples uniquely within the database. Foreign key is an attribute or a set of attributes within on relation that matches the candidate key of some relation. The degree of a relation is the number of tuples it contains. Discussion Questions 14 SJSU – CmpE --- M.E. Fayad

More Related