1. 603 Database Systems Senior Lecturer: Laurie Webster II, M.S.S.E.,M.S.E.E., M.S.BME, Ph.D., P.E. Lecture 21 A First Course in Database Systems

2. SQL Union, Intersection, and Difference in SQL: Union   Intersection   Difference  - Words like UNION are used between two queries, and those queries must be parenthesized.

3. SQL Suppose we wanted the names and addresses of all female move stars who are also movie executives with a net worth over $10,000,000. Using the following two relations: MovieStar ( name, address, gender, birthdate) MovieExec ( name, address, cert#, netWorth) Develop the SQL query!

4. SQL Using the following two relations: MovieStar ( name, address, gender, birthdate) MovieExec ( name, address, cert#, netWorth) 1)(SELECT name, address 2)FROM MovieStar 3)WHERE gender = ‘F’) 4)INTERSECT 5)(SELECT name, address 6)FROM MovieExec 7)WHERE netWorth > 10000000 ) ;

5. SQL 1)(SELECT name, address 2)FROM MovieStar 3)WHERE gender = ‘F’)  yield a relation whose schema is (name, address) and whose tuples are the names and addresses of all female movie stars.

6. SQL 5)(SELECT name, address 6)FROM MovieExec 7)WHERE netWorth > 10000000 ) ;  produce the set of “rich” executives, those with net worth over $10,000,000. This query also yields a relation whose schema has the attributes name and address only.

7. SQL Since the two schemas are the same, we can intersect them, and we do so with the operator of line 4). We can take the difference of two sets of persons, each selected from a relation. The query (SELECT name, address, FROM MovieStar) EXCEPT (SELECT name, address, FROM MovieExec) ; ==>names and addresses of movie stars who are not also movie executives, regardless of gender or net worth.

8. SQL Set Operations UNION in SQL: Make a list of all project numbers for projects that involve an employee whose last name is ‘Smith’, either as a worker or as a manager of the department that controls the project. SELECTPNUMBER FROMPROJECT, DEPARTMENT, EMPLOYEE WHEREDNUM=DNUMBER AND MGRSSN=SSN AND LNAME=‘Smith’) UNION SELECTPNUMBER FROMPROJECT, WORKS_ON, EMPLOYEE WHEREPNUMBER=PNO AND ESSN=SSN AND LNAME=‘Smith’)

9. SQL First SELECT retrieves projects that involves a “Smith’ as a manager of the department that controls the project Second SELECT retrieves projects that involves a ‘Smith’ as a worker on the project UNION operation on the two SELECTs is result desired

10. The Deductive Databases Some query languages for the relational model resemble a logic more than they do the algebra that we introduced earlier. The logic-based languages appear to be difficult for many programmers to grasp. We will discuss Deductive Databases, which is the intersection of databases, logic, and artificial intelligence or knowledge bases.

11. Deductive Databases A deductive database system is a database system that includes capabilities to define (deductive) rules, which can deduce or infer additional information from the facts that are stored in a database. Because part of the theoretical foundation for some deductive database systems is mathematical logic, such rules are often referred to as logical databases.

12. Deductive Databases In a deductive database system, we typically specify rules through a declarative language - a language in which we specify what to achieve rather than how to achieve it. An inference engine ( or deduction mechanism) within the system can deduce new facts from the database by interpreting these rules. The model for deductive databases is closely related to the relational data model, and particularly to the domain relational calculus formalism.

13. Deductive Databases Deductive Database is also related to the field of logic programming and the Prolog language. The deductive database work based on logic has used Prolog (Programming in Logic) as a starting point. A variation of Prolog called Datalog is used to define rules declaratively in conjunction with an existing set of relations, which are themselves treated as literals in the language. The basic constructs of logic programming: terms, statements

14. Deductive Databases There are three basic statements in logic programming: 1)facts 2)rules 3)queries Facts The simplest kind of statement is called a fact Fact ==> stating that a relationship holds between objects

15. Deductive Databases Fact Example: father ( abraham, isaac). ==> Abraham is the father of Isaac, or that the relation father holds between the individuals named abraham and isaac. Another name for relationship is predicate.

16. Deductive Databases Names of individuals are know as atoms. Similarly plus (2,3,5) ==> expresses the relationship that 2 plus 3 is 5. plus is a predicate! The familiar plus relationship can be realized via a set of facts that defines the addition table.

17. Deductive Databases An initial segment of the addition table is: plus(0,0,0).plus(0,1,1). plus (0,2,2). plus(0,3,3). plus(1,0,1). plus(1,1,2). plus(1,2,3). plus (1,3,4). Notice the period after each sentence. The table above is a segment of the definition of plus!

18. Deductive Databases Syntactic conventions for logic programming: 1)case convention Names of both predicates and atoms in facts begin with a lowercase letter (italicized when they appear in running text). 2)program A finite set of facts constitutes a program. This is the simplest form of a logic program.

19. Deductive Databases Syntactic conventions for logic programming: 2)program (continued) A set of facts is also a description of a situation. This insight is the basis of database programming !

20. Deductive Databases Example Database of family relationships from the Bible: father(terach, abraham). male(terach). father(terach, nachor).male(abraham). father(terach, haran). male(nachor). father(abraham, isaac). male(haran). father(haran, lot). male(isaac). father(haran, milcah). male(lot). father(haran, yiscah). female(sarah). female(milcah). mother( sarah, isaac). female(yiscah).

21. Deductive Databases father(terach, abraham). male(terach). mother( sarah, isaac). female(yiscah). The predicates father, mother, male, female express the obvious relationships.

22. Deductive Databases A second form of statement in a logic program is a query. Queries are a means of retrieving information from a logic program. A query asks whether a certain relation holds between objects.

23. Deductive Databases Query Example: father (abraham, isaac)? ==> asks whether the father relation holds between abraham and isaac.

24. Deductive Databases father (abraham, isaac)? Given the facts presented earlier the answer to this query is YES! Note: statement of fact or question

25. SQL Next Lecture MORE Deductive Databases