1. Object Query Language (OQL) Marián Kamenišťák MFF – UK Praha 26.11.2003

2. Úvod podobný SQL jazyku založený na ODMG štandarte Architektúra: Nástroje: C, C++, Java, … DB engine: napr. O2 engine & store Interfaces: O2ODBC, O2Cobra,..

3. Základné dotazy (C++) class item {String what; double price;}; class client {String name; Array order; int amount(); };

4. Základné dotazy Select distinct e.salary from e in Schema.employees where e.family != nil and e.position = “reporter”; … where count(e.children) >=1; … group by … having … … order by … (vracia pole) existujú agregačné fcie: min, max, sum, avg

5. Tvorenie výsledkov Define MyEmployees as select struct(employee: struct(e.name, position: e.post), salary: e.salary) from e in Company.employees; element (select e from e in MyEmployees where e.salary>150000);

6. Množinové operátory Zjednotenie(+): MyEmployees + YourEmployees Prienik (*) Rozdiel (-)

7. Konverzie listtoset(Companies[2].clients) Naopak: select e from e in MyEmployees order by e.name; z kolekcie kolekcií na plochú kolekciu: flatten(select e.clients from c in Companies); flatten(list(list(1,2), list(1,2,3))) -> list(1,2,1,2,3) ‘string’ like ‘%nice_%’

8. Preddefinované typy kolekcií Set - mna set(1,2,5) Bag - multimna bag(1,2,2,3,3) Varray - dynamické pole List - Varray s metódami pre manipuláciu (insert, delete,..) list(1,2,2,3); list(3..5) Ref - perzistentný pointer

9. Pokročilé OQL class Person { String name; Date birth; set > childs inverse parents; set > parents inverse childs; Person(); //constructor void birth(ref child); //narodenie d. virtual set activities(); }

10. OQL class Employee:Person{ //podtrieda float salary; virtual set activities();//predefinit. }; Join: Select p from p in Persons, b in (select a.building from a in Apartments) Where p.name = b.address.street;

11. OQL – Data manipulation select struct (me:p.name, address:p.lives_in.building.address; childs: (select struct(name: c.name, address: c.lives_in.building.address) from c in p.children) ) from p in Persons; //adresy detí cez všetky osoby.

12. OQL Polymorfizmus napr. mna Persons obsahuje prvky tried Preson, Employee, Student. Potom sa virtuálna metóda activities() vykoná pre konkrétnu triedu. Select ((Student)p).grade from p in Persons where “lecture” in p.activities;

13. OQL define salary_map as select street, average_salary: avg(select p.e.salary from partition p) from e in Employees group by e.lives_in.building.address.street; //returns Bug<struct {String street; float avg_salary;>};

14. OQL define sorted_salary_map as select s from s in salary_map order by s.average_salary List<struct {String street; float avg_salary;} > sorted_salary_map[2].street;

15. OQL define Jakes as select x from Students x where x.name = “Jake”; define Jake as first(element( select x from Students x where x.name = “Jake”));  //first, last operators in list

16. OQL Prechádzanie štruktúrami:  person.name == person->name //rovnaké  Jake->woman!=nil and Jake->woman->name=Carol Dereferencie  p1 = p2 je pravda, ak ukazujú na rovnaký objekt  *p1 = *p2 je pravda, ak majú rovnaké hodnoty

17. OQL - group by select * from Employees e group by low: e.salary<1000, medium: e.salary>=1000 and e.salary<2000, high: e.salary>=2000; Vytvorí pomenované partition bugy

18. Literatúra ODMG OQL user manual 5.0 feb. 1998