Object Oriented Databases Bringing objects into databases

An object database schema ADDRESS Street:String City:String PERSON SS#:String Name:String Address:Address EMPLOYEE ISA PERSON Salary:Integer Boss:Employee Departments:{Department} COMPANY Name: String Head quarters: Address Departments: {Department} CEO: Employee DEPARTMENT Name:String Office:Address Boss:Employee Employees:{Employee}

An object database query SELECT e.Name FROM e in EMPLOYEE, d in DEPARTMENT WHERE e in d.Employees AND e.Address.City = d.Office.City

Object database concepts Simple values Complex values Objects TypesClasses 25 #11‘bo’ {25,7} [a:1,b:2] PersonCar [ss#:String,age:Integer]

Simple and complex values A is the set of all attributes O is the set of all object identifiers D is the union of integers, reals, strings, and booleans Elements in O U D are called simple values Elements of the form [A 1 :w 1, …, A n :w n ] are tuple values where A i is an attribute and w i a value Elements of the form {w 1, …, w n } are set values A complex value is a tuple value or a set value

Objects An object is a pair (o, w) o is an object identifier w is a value

Examples of objects A = {SS#, Name, Address, Main office, Departments, CEO} O = {#11, #12, #13, #14, #21, #31, #41} z(#11, [SS#: ‘ ’, Name: ‘Bo Ek’, Address: [Street: ‘Storg. 4’, Town: ‘Karlstad’]]) z(#14, [Name: ‘Acme’, Head office: [Street: ‘Storg. 12’, Town: ‘Karlstad’], Departments: {#21, #31, #41}, CEO: #11])

Value and object equality zValue equality Two objects are equal if their values are equal (o 1, w 1 ) = (o 2, w 2 ) iff w 1 = w 2 zObject equality Two objects are equal if their object identifiers are the same (o 1, w 1 ) = = (o 2, w 2 ) iff o 1 = o 2

Surface and deep equality Surface equality: equality without substituting object references Deep equality: equality after substituting object references by values w 1 = [A: o 1 ] w 2 = [A: o 2 ] (o 1, w) (o 2, w) where o 1  o 2 w1 not surface equal to w2 w1 deep equal to w2

Surface and deep equality w 1 = [A: o 1, B: 25] w 2 = [A: o 2, B: o 3 ] w 3 = [A: o 2, B: o 4 ] (o 1, 25) (o 2, 50) (o 3, 25) (o 4, o 1 ) w 1 deep equal to w 2 ? w 1 deep equal to w 3 ? w 2 deep equal to w 3 ?

Types and classes Intuitions: zValues with the same structure are described by a type zObject identifiers for similar objects are grouped into a class A class can be associated with a type to specify the structure of the objects of the class A class can be used as a type for typing references between objects

Types Let K be a set of classes. zBase types: {integer, float, string, boolean} zReference types: K zTuple types: elements of the form [A 1 :T 1, …, A n :T n ], where A i is an attribute and T i en typa type zSet types: {T}, where T is a type A complex type is a tuple type or a set type

An example type K = {Car, Company, City} EMPLOYEE SS#:Integer Name:String Lives in:City Works at:Company Owns:{Car} Base type Reference type Set type Tuple type

Object database schema An object database schema consists of: zA set of class names K zFor each k in K, a type that specifies the structure of k

Object database extension zGiven an object database schema S, an extension for S associates each k in K with a set of object identifiers

An example extension Animal Mammal Bird Dog K #1 #2 #3 #4 #5 #1 #2 #3 #4 #5

Types, classes, objects, and values Person Bil #11 #12 #22 #21 [Regnr: String, Färg: String, Ägare: Person] [Pnr: String, Namn: String, Lön: Integer] [Pnr: ‘ ’, Namn: ‘Per Svensson’, Lön: 25000] [Regnr: ‘ABC123’, Färg: ‘Röd’, Ägare: #11] K Types W O

Query languages zAllmängiltighet zDeklarativitet zOptimerbarhet zSlutenhet zUttryckskraft zUtvidgningsbarhet

Two simple queries SELECT a FROM a in EMPLOYEE WHERE Salary > SELECT SS#, Name FROM EMPLOYEE WHERE Salary > 20000

Path expressions (dot notation) SELECT Name FROM Company WHERE Head_quarters.City = “London” SELECT Name, Head_quarters.Street FROM Company WHERE Head_quarters.City = “London”

Sets in queries What does this query mean? SELECT c FROM c in COMPANY WHERE CEO IN (SELECT e FROM e in EMPLOYEE WHERE Employee.Address.City = “Lund”)

Sets in queries SELECT c.Name FROM c in COMPANY WHERE c.Departments.Office.City = {“London”, “Lund”}

Sets and dot notation SELECT c.Departments.Employees.Salary FROM c in COMPANY c.Departments.Employees.Salary {f1, f2, f3} {a1, a2} {a3, a4} {a5} {f1, f2, f3} {{a1, a2}, {a3, a4}, {a5}} ? {a1, a2, a3, a4, a5} ?

Sets and dot notation SELECT c.Departments.Employees.Salary FROM c in COMPANY {f1, f2, f3} {a1, a2} {a3, a4} {a5} Answer: {100, 150, 200}

Exercises zWhich employees work at the same departments as their bosses? zWhich (pair of) employees work at the same departments? zWhich companies do not have any employee living in London? zIn which companies do all employees live in London?

Exercises zWhich employees work only at departments that are situated in London? zWhich employees do not work at a department in London? These queries become harder if the attribute “Departments” is removed. Try to write the queries also without this attribute.

Exercises zIn which companies are there employees who live in cities where the company does not have any department? zIn which companies does the boss of each employee live in the same city as the employee?

zWhich employees work at the same departments as their bosses?

zWhich (pair of) employees work at the same departments?

zWhich companies do not have any employee living in London?

zIn which companies do all employees live in London?

zWhich employees work only at departments that are situated in London?

zWhich employees do not work at a department in London?

zIn which companies are there employees who live in cities where the company does not have any department?

zIn which companies does the boss of each employee live in the same city as the employee?

zWhich employees work at the same departments as their bosses? SELECT e.Name FROM e in EMPLOYEE WHERE e.Departments = e.Boss.Departments

zWhich (pair of) employees work at the same departments? SELECT e1.Name, e2.Name FROM e1 in EMPLOYEE, e2 in EMPLOYEE WHERE e1.Departments = e2.Departments

zWhich companies do not have any employee living in London? SELECT c FROM c in COMPANY WHERE ‘London’ NOT IN c.Departments.Employees.Address.City

zIn which companies do all employees live in London? SELECT c FROM c in COMPANY WHERE c.Departments.Employees.Address.City = {‘London’}

zWhich employees work only at departments that are situated in London? SELECT e.Name FROM e IN EMPLOYEE WHERE NOT EXISTS (SELECT d FROM DEPARTMENT WHERE e in d.Employees AND d.Office.City <> ‘London’) SELECT e.Name FROM e in EMPLOYEE WHERE e.Departments.Office.City = {‘London’}

zWhich employees do not work at a department in London? SELECT e.Name FROM e in EMPLOYEE WHERE NOT EXISTS (SELECT d FROM d in DEPARTMENT WHERE e in d.Employees AND d.Office.City = ‘London’) SELECT e.Name FROM e in EMPLOYEE WHERE ‘London’ NOT IN e.Departments.Office.City

zIn which companies are there employees who live in cities where the company does not have any department? SELECT c FROM c IN COMPANY WHERE c.Departments.Employees.Address.City MINUS c.Departments.Office.City <> Ø

zIn which companies does the boss of each employee live in the same city as the employee? SELECT c FROM c in COMPANY WHERE NOT EXISTS (SELECT e FROM e in EMPLOYEE WHERE e IN c.Departments.Employees AND e.Boss.Address.City <> e.Address.City)

zWhich employees work at a department in a city where they do not live? SELECT e.Name FROM e in EMPLOYEE, d in DEPARTMENT WHERE e in d.Employees AND d.Office.City <> e.Address.City

zWhich employees live in the same city as (at least one of) their boss(es)? SELECT e.Name FROM e in EMPLOYEE, d in DEPARTMENT WHERE e in d.Employees AND e.Address.City = d.Boss.Address.City