Lecture 3

1. Lecture 3 Object database standards, languages and design OODBs

2. Development of Object-based Systems • Object-Oriented Database Systems • An alternative to relational systems • Application domains where objects play central role • Heavily influenced by object-oriented programming languages • An attempt to add DBMS functionality to a programming language environment OODBs

3. Development of Object-based Systems - cont. • Object-Relational Database Systems • An attempt to extend relational databases • Broader set of applications • Provide bridge between relational and object-oriented systems OODBs

4. Why a Standard? • Portability from one vendor (system) to another • Interoperability between systems based on different vendor products easier OODBs

5. Object Data Management Group(ODMG) • ODMG-93 or ODMG 1.0; ODMG 2.0 (1997) • Parts • Object model • Object definition model (ODL) • Object query language (OQL) • Bindings to OO programming languages OODBs

6. Unified Modeling Language (UML) • DEC • HP • IBM • Unisys • I-Logix • Intellicorp • MCI Systemhouse • TI • Microsoft • Icon Computing • Rational Software • Oracle • Consortium of vendors including • UML 0.9 (1996); UML 1.1 (1997) • Unified as to • Differences in Modeling Languages • Differences in Perspectives OODBs

7. ODMG Object Model • Literal • State (or value) {constant} • No OID • May have complex structure • Types of literals • Atomic - Simple, e.g., 10.2 - Structured, e.g. Date (19, May, 2001) • Collection, e.g. days of the week (Sun, Mon, …, Sat) OODBs

8. ODMG Object Model • Object • Identifier (OID) • Name (optional) • Lifetime (persistent or transitory) • Structure • How constructed • Atomic • Collection: t a type, k a key, v a value • Set <t> • Bag <t> • List <t> • Array <t> • Dictionary <k, v> • Specified by interface OODBs

9. Interface Definitions from ODMG Object Model • Object Data Language • ODL OODBs

10. interfaceObject { … boolean same_as(in Object other_object); Object copy(); void delete(); } Examples:Object – inherited by all objectsDate – structured literal Date is subtype of Object (i.e., inherits from). interfaceDate:Object { enum Weekday {Sunday, Monday, …, Saturday}; enum Month {January, February, …, December}; unsigned short year(); unsigned short month(); unsigned short day() … boolean is_equal(in Date other_Date); boolean is_greater(in Date other_Date); … } Operations are inherited by user-defined objects. OODBs

11. Structured Literals Time Timestamp Interval Collection Objects Collection Iterator Set Bag List Array Association Dictionary See text for the following examples: OODBs

12. Object Interfaces • All objects inherit basic interface of Object using dot notation: • o.same_as(p) – true if p is the same as o • p = o.copy() – create copy p of object o • o.delete() – delete object o • May also use arrow notation: • o->same_as(p) – true if p is the same as o OODBs

13. Class Definition Examples:Employee ClassEmployee ( extent all_employees key ssn ) { attribute string name; attribute string ssn; attribute date birthdate; attribute enum Gender{M,F}sex; relationship Departmentworks_for inverse Department::has_emps; void reassign_emp(in string new_dname) raises(dname_not_valid) ; } Note that both “works_for” and inverse relationship, “has_emps”, are specified. OODBs

14. Class Definition Examples:Department ClassDepartment ( extent all_departments key dname, dnumber ) { attribute string dname; attribute short dnumber; attribute struct Dept_Mgr{Employee manager, date startdate} mgr; attribute set<string> locations; attribute struct Projs {string projname, time weekly_hours} projs; relationship set<Employee> has_emps inverse Employee::works_for; void add_emp(in string new_ename) raises(ename_not_valid); void change_manager(in string new_mgr_name) in date startdate); } OODBs

15. Relationships works_for andhas_empsbetweenEmployee and Department • ClassEmployee • {… • relationship Departmentworks_for inverse Department::has_emps; • } • ClassDepartment • {… • relationship set <Employee> has_emps inverseEmployee::works_for; • } OODBs

16. COMPANY database in ODL Diagrammore details on page 680 in book works_for employs supervisee EMPLOYEES DEPARTMENT manages managed_by located_at supervisor manager department controls has_ dependents MANAGE_DEPT works _on has_ departments LOCATION employee has_ projects WORKS_ON_PROJECT project controlled _by dependent_of located_at employees_on DEPENDENT PROJECT OODBs

17. Interface (e.g. Date) Abstract behavior, specification via operation signatures Noninstantiable (i.e. cannot have object matching description) Used via inheritance (behavior inheritance “:”) Class (e.g. Employee) Abstract behavior Abstract state Instantiable Object Types: Interfaces vs. Classes • Terminology • Behavior: operations • State: properties (attributes & relationships) OODBs

18. Behavior Inheritance Supertype must be interface Subtype may be interface or class Denoted by “:” Multiple inheritance permitted EXTENDS Inheritance Inherit state and behavior among classes Both supertype and subtype must be classes Multiple inheritance not permitted Specified by extends keyword Inheritance Relationships: Behavior vs. Extends OODBs

19. Example: PersonUNIVERSITY Database ClassPerson ( extent persons key ssn ) { attribute struct Pname {string fname, string mname, string iname} name; attribute string ssn; attribute date birthdate; attribute enum Gender{M,F}sex; attribute struct Address {short no, string street, …, short zip} short age(); } OODBs

20. Example: FacultyUNIVERSITY Database ClassFaculty extendsPerson ( extent faculty) { attribute string rank; attribute float salary; attribute string office; attribute string phone; relationship Department works_in inverse Department::has_faculty; relationship set<GradStudent> advises inverse GradStudent ::advisor; relationship set<GradStudent> on_committee_of inverse GradStudent ::committee; void give_raise(in float raise); void promote(in string new_rank); } Extends inheritance from Person OODBs

21. Student extends Person Degree GradStudent extends Student Department Course Section CurrSection extends Section Grade Example: other classesUNIVERSITY Database OODBs

22. Factory Objects • Used to generate individual objects • Examples • ObjectFactory • DateFactory • DatabaseFactory • Include new() operation Interface ObjectFactory { Object new(); } OODBs

23. Database Factory interfaceDatabase { void open(in string database_name); void close(); void bind( in any some_object, in string some_object); Object unbind(in string name); Object lookup(in string object_name) raises(ElementNotFound); } interfaceDatabaseFactory { Database new(); } OODBs

24. Object Database Standards, Languages, and DesignPart II: Object Query language (OQL) OODBs

25. Object Query Language (OQL) • “Bring the best of SQL to the object world.” • Syntax similar to SQL • Plus additional features • Works with programming languages where ODMG has defined bindings • Java, C++, Smalltalk • Returns object matching type system of that language • May implement class operations in these languages • SQL3 – “Bring the best of the object-oriented world to the relational world.” OODBs

26. Movies Example: Movies, Stars, Studios Star name address street city Movie title year length /* in minutes */ filmType:{color, blackAndWhite} lengthInHours starNames otherMovies stars starredIn 1..* 1..* ownedBy owns 1..* 1..1 Studio name Set of stars of this movie. Other movies by star of this movie. OODBs

27. Movies Example: Movies, Stars, Studios classMovie (extent Movieskey (title, year)) { attribute string title; attribute integer year; attribute integer length; /* in minutes */ attribute enumeration (color, blackAndWhite) filmType; relationshipset<Star> stars inverse Star :: starredIn; relationship Studio ownedBy inverse Studio :: owns; float lengthInHours() raises(noLengthFound); starNames(out set<String>); otherMovies(in Star, out set(<Movie>) raises(noSuchStar); }; OODBs

28. ClassStar (extent Stars key name) { attribute string name; attribute struct Addr; {string street, string city} address; relationshipset<Movie> starredIn inverse Movie :: stars; }; Movies Example, contd. ClassStudio (extent Studios key name) { attribute string name; relationshipset<Movie> owns inverse Movie :: ownedBy; }; OODBs

29. Specifying data from ODB • Path expression • Dot notation similar to structure in programming language, • e.g., o.a attribute a of object o. • Select-From-Where expression • Similar to SQL. • References are to data classes, not relations. • Integrated directly into host language. OODBs

30. Path Expressions Assume myMovie a host-language variable, value a Movie object. • myMovie.length - length of the movie. • myMovie.lengthInHours() - real number, computed as length in minutes. • myMovie.stars – set of Star objects related to myMovie by relationship stars. • myMovie.starNames(myStars) – returns no value, sets output variable myStars of method starNames to set of strings with names of the stars of the movie. • myMovie.ownedBy.name – string that is name of studio owning myMovie. OODBs

31. Select-From-Where Expressions, I • Year of the movie Gone with the Wind. select m.year from m in Movie where m.title = “Gone with the Wind”; • Bag containing names of stars of Casablanca. select s.name from m in Movies, s in m.stars where m.title = “Casablanca”; • Set containing names of stars of Disney movies. select distinct s.name from m in Movies, s in m.stars where m.ownedBy.name = “Disney”; Might contain duplicates, therefore bag. Must name all components in hierarchy, i.e., Movies & stars. No duplicates, therefore set. OODBs

32. Select-From-Where Expressions, II Result is set of structs. • Pairs of stars living at the same address. select distinctstruct(star1: s1, star2: s2) from s1 in Stars, s2 in Stars where s1.addr = s2.addr and s1.name < s2.name; • Set containing names of stars of Disney movies, using subquery. Select distinct s.name from (select m from m in Movies where m.ownedBy.name = “Disney”) dm, sin dm.stars; • Set of all Disney movies, ordering results by length and title. select m from m in Movies where m.ownedBy.name = “Disney” order bym.length, m.title; Bag of all Disney movies. Stars in those movies. List of Movies in ascending order OODBs

33. Select-From-Where Expressions, III • Set containing names of stars of Disney movies, using existential quantifier. select distinct s.name from s in Stars where existsm in s.starredIn : m.ownedBy.name = “Disney”; • Set containing names of stars that have appeared only in Disney movies, using universal quantifier. select distinct s.name from s in Stars where for allm in s.starredIn : m.ownedBy.name = “Disney”; OODBs

34. Select-From-Where Expressions, IV Want bag of lengths, not set. • Average length of all movies. Avg( select m.length from Movies m); • Table of lengths of movies for each studio for each year. select std, yr, sumLength: sum( select p.m.length from p in partition) from m in Movies group by std: m.studio, yr: m.year; • Table of lengths of movies for each studio for each year where studio produced at least one movie of over 120 minutes in that year. select std, yr, sumLength: sum( select p.m.length from p in partition) from m in Movies group by std: m.studio, yr: m.year havingmax(select p.m.length from partition p) > 120; OODBs

35. Views • View returning Set containing movies by studio studio. • define moviesFromStudio(studio) as • select m • from m in Movies • where m.ownedBy.name = studio; Do not need “distinct m”, since Movies is already a set. OODBs

36. Returning a single element • Bag or Set (if distinct included) normally returned. • May want singleelement. • Return Moviewithname Casablanca. Element (select m from m in Movies where m.title = “Casablanca”); OODBs

37. Find names of those who starred in allDisney movies. Star name address street city Movie title year length /* in minutes */ filmType:{color, blackAndWhite} lengthInHours starNames otherMovies stars starredIn 1..* 1..* ownedBy owns 1..* 1..1 Studio name Idea: select s.name from s in Star where for all DisneyMovies exists ds in DisneyMovies.stars with same name; OODBs

38. Find names of those who starred in allDisney movies:First attempt. • Using “if p then q”. select s.name from s in Star wherefor all m in Movie : (if m.ownedBy.name = ‘Disney’ thenexists s1 in m.stars : s1.name = s.name); • Converting “if p then q” to “~p or q”. select s.name from s in Star wherefor all m in Movie : (m.ownedBy.name != ‘Disney’ or exists s1 in m.stars : s1.name = s.name); OODBs

39. Find names of those who starred in allDisney movies:Using a view of all Disney movies. View returning Set of Disney movies. define DisneyMovies as select m from m in Movies where m.ownedBy.name = ‘Disney’; • Query for stars using the DisneyMovies view. select s.name from s in Star wherefor all dm in DisneyMovie : (exists s1 in dm.stars : s1.name = s.name); OODBs

40. Find names of those who starred in allDisney movies:Using the Movie.starNamesfunction. Change • starNames(out set<String>) to a function • set<String> starNames() • Query for stars using the DisneyMovies view and starNames() function. select s.name from s in Star wherefor all dm in DisneyMovie : s.name in dm.starNames(); OODBs