1 advanced database topics copyright © ellis cohen 2002-2005 objects and relational databases these...

1

Advanced Database Topics

Copyright © Ellis Cohen 2002-2005

Objects and Relational Databases

These slides are licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License.

For more information on how you may use them, please see http://www.openlineconsult.com/db

© Ellis Cohen 2002-2005 2

Topics

Object-Relational Mapping

OR Mapping Approaches & Issues

Object-Relational Databases

Referenced Objects & Navigation

Contained Objects

Nested Tables

Nested Collections


Drivers for OO & RDB Integration

• Persistent Object Storage– Need for a way to easily save and

restore computation state of programs built via OOPL's using standard RDBs

• OO Programming for RDB Data– Treat rows of a table (plus asssociated

data in other tables) like an object for programmatic access & modification

• OO Database Programming– Brings benefits of OO approach to RDB's


Object-Relational Mapping


OR Mapping Motivations

• Want to persist OO data so it is queryable (e.g. w OQL), but using the standard RDB your organization is already using.

• Want to write OO programs that use and manipulate data stored in an RDB.– OO programmers did this anyway before

advent of technologies like JDO.

– Painful enough that the correspondence between relations & objects was referred to as an impedance mismatch.


Object Model & Actual RDB

30 SALES

10 ACCOUNTING

50 SUPPORT

deptno dname

Deptsempno name addr deptno

7499 ALLEN ... 30

7654 MARTIN … 30

7844 TURNER … 30

7212 LAVICH …

7698 BLAKE … 10

7986 STERN … 10

Emps

empno: 7499name: ALLENaddr: …dept:

empno: 7654name: MARTINaddr: …dept:

deptno: 30dname: SALES


OR Mapping Approaches

Programmatic Approach:Write the code to transform the object

• when loading it into the cache, and • when persisting it to the RDB,

Declarative/Automatic Approach:

Provide a description of how the OOPL & RDB models are mapped to one another.

The mapping layer uses the description to automatically transform the representations on object loading and persistence!

The mapping layer translates OO queries (e.g. OQL, HQL, JDOQL, OPath) automatically into SQL

The representation of an object in an OOPL may be quite different from its representation

when stored in an RDB


Current Systems (1)

JDO– Java standard– Uses transparent persistence– Many commercial implementations,

including Kodo & ObjectBridge– Uses JDOQL, a limited Java-based query

language (improved in 2.0)– JDO 2.0 adds significant support to

control the OR mapping

Castor– Java-based system using JDO API– Will use OQL as its query language


Current Systems (2)

Hibernate– Most popular Java-based system– Uses explicit persistence– Uses HQL, a limited query language

derived from OQL

ObjectSpaces– Microsoft's system for .NET– Uses transparent persistence– Use OPath query language, loosely

derived from XML's XPath

© Ellis Cohen 2002-2005 10

Mapping OQL to SQL

SELECT e.ename, e.dept.dnameFROM emps e

in OQL is mapped to the SQL:

SELECT e.ename,(SELECT d.dname FROM Depts d WHERE e.deptno = d.deptno)FROM Emps e

A good optimizer will treat this as equivalent to

SELECT ename, dname FROM Emps NATURAL JOIN Depts

© Ellis Cohen 2002-2005 11

Early OPathFilters placed in square brackets used instead of WHERE clauses

Employee[empno = 3417]• The employee whose empno is 3417

Employee[job = 'ANALYST']• The employees who are analysts

Navigation represented by a dot; can be applied to a collection

Employee[dept.dname = 'RESEARCH']Dept[dname = 'RESEARCH'].empls

• Employees in the research departmentEmployee[job = 'CLERK'].dept.dnameDept[empls.job = 'CLERK']

• Departments that have clerks

Early versions of OPath were very closely related to XML's XPath query language.

OPath has since evolved away from this model

© Ellis Cohen 2002-2005 12

Mapping Early OPath to SQL

Employee[job = 'CLERK'].dept.dname

in Early OPath is mapped to the SQL:

SELECT DISTINCT (SELECT d.dname FROM Depts d WHERE e.deptno = d.deptno)FROM Emps eWHERE job = 'CLERK'

A decent optimizer will treat this as equivalent to

SELECT DISTINCT dname FROM Emps NATURAL JOIN Depts WHERE job = 'CLERK'

© Ellis Cohen 2002-2005 13

OR MappingApproaches & Issues

© Ellis Cohen 2002-2005 14

OOPL RDB Mapping Approaches (1)

OOPL model(ODL / Java / C#) RDB Model

OOPL RDB Map

OOPL model(ODL / Java / C#)

RDB Model

RDB OOPL Map

Generate

Generate

Start with

Start with

Define

Define

© Ellis Cohen 2002-2005 15

OOPL RDB Mapping Approaches (2)


OOPL / RDB Map


ER RDB & OOPL

Map

ER Model

Generate Generate

Just Define

Start withStart with

Start with

Define

© Ellis Cohen 2002-2005 16

Mapping RDB OOPLGiven a legacy RDB

Design the corresponding OOPL.

•How are FK's treated– retain and/or convert to relationships– one or two-way relationships

•Specify field types (when not obvious)•Mapping enums•Generate OIDs

– Unique to class• Primary Key

– Unique to application (allows application to use OIDs to retrieve objects)

• TableName + PrimaryKey• ROWIDs

– Globally unique (OIDs can be used to retrieve objects across a global network)

• ip address + DB instance + app name + unique-to-application

© Ellis Cohen 2002-2005 17

Example RDB OOPL Spec<mappings OID="table" …>

--getOid will return tableName || '|' || primaryKey <class name="Employee" keyclass="Emps">

<usetable name="Emps">-- build Employee fields from Emps columns<field name="empno"/><field name="ename"/><field name="salary" column="sal"/>

-- Emps' sal column should become Employee's salary field<field name="job" type="int">

<mapval from="MANAGER" to="1"/>-- Emps job='MANAGER' Employee job=1

<mapval from="CLERK" to="2"/>…

</field><field name="mgr" map="ref"/>

-- Emps mgr is a foreign key for an Emps-- so in Emps, have it hold a reference to an Employee

<field name="deptno" field = "dept" map="FK"/></usetable>

</class>

© Ellis Cohen 2002-2005 18

Mapping OOPL/ER RDB

Given a new OO or ER modelDesign the corresponding RDB.

•Determining Primary Keys– Object class field– Automatically generated surrogate keys

• unique to class, database, GUIDs

•Specify column types & constraints•Generate OIDs

– Same as for RDB ER– Related to how PK's are determined

•Converting References– FK to primary key or other unique columns

•Mapping Enums

© Ellis Cohen 2002-2005 19

Example OOPL RDB SpecExample OOPL RDB Mapping (non-standard)

<mappings PK="GUID" OID="PK" …>--all tables will get globally unique surrogate PK's, which will be returned as OIDs

<table name="Emps"><useclass name="Employee">

-- build Emps column from Employee fields, with empno as PK<column name="empno" unique="T" len="5"/><column name="ename" len="20"/><column name="sal" field="salary" len="8.2"/>

-- Employee's salary field should become Emps' sal column<column name="job" type="varchar" len="12">

<mapval from="1" to="MANAGER"/>-- Employee job=1 Emps job='MANAGER'

<mapval from="2" to="CLERK"/>…

</column><column name="mgr" map="FK"/>

-- Employee's mgr is a ptr to an Employee-- so in Emps, have mgr instead hold a foreign key for an Emps

<column name="deptno" field = "dept" map="FK"/></useclass>

</table>

© Ellis Cohen 2002-2005 20

Using GUIDs as PKs

Initial Design: OOPL or ODLGoal: Design an RDB Schema which

associates OIDs with each tuple

Emps

304729… 20 Accounting

8B6B2A.. 30 Research

516123.. 50 IT

deptoid deptno deptnam Depts

empoid empno deptoid

A134E2… 20693 … 304729…

C0E11A… 19419 304729…

D44472… 82331 8B6B2A..

7C91EE… 30492 304729…

437A23… 93200 516123..

Includes deptoid instead of deptno

What are pros and cons of using OIDs as PK/FKs?

© Ellis Cohen 2002-2005 21

Object-Based Integration

OODB

RDB

Files

CORBA Service

Client

Issue OQL Query

OQL

CORBA R

equest

Read/Parse

SQL/SQLX

Object Integration Server

• Develop Object Model for each data source

• Maps OQL to distributed native queries/request

• Maps combined results to objects

MDDBMDX

© Ellis Cohen 2002-2005 22

Integrated Relational Querying

Use an RDB, View both as OO Data– User still sees OO data as OO. Its mapping to the

RDB is hidden– User sees an OO representation of the relational

data as well, based on a hidden mapping– User queries all data with OQL, automatically

mapped to SQL

Use an RDB, View both as Relational Data– User sees relational data as is– User sees OO data in terms of its relational

representation, based on a public mapping – User uses SQL to query all data

Use an Object-Relational Database– RDB w user-defined object data types + references– Incorporates navigation into SQL

Suppose we have both persistent OO and Relational data. How can we arrange to do queries joining both of

them?

© Ellis Cohen 2002-2005 23

Object-RelationalDatabases(ORDBs)

© Ellis Cohen 2002-2005 24

ORDBs

Object-Relational Databases integrate an Object Model with the Relational Model.

• Users can extend the built-in data types (number, date, etc.) with arbitrary object types.

• Columns can hold references to objects.

• SQL is extended to support field access and navigation just as in OQL.

• Tables (containing objects or references to object) are the primary (or sometimes only) collection type.

• Moreover, objects are not stored independently as in OODBs; they must be placed in tables.

© Ellis Cohen 2002-2005 25

Rows as Objects/Entities

empno: 7654name: MARTINsal: 1250comm: 1400

an Employee Object

It can be useful to think of each row as an object or entity (i.e. an instance of an entity class) and the table as a collection of these objects

The columns of the table correspond to the instance variables for each object

It can be useful to think of each row as an object or entity (i.e. an instance of an entity class) and the table as a collection of these objects

The columns of the table correspond to the instance variables for each object

empno name sal comm

Emps

7499 ALLEN 1600 300

7654 MARTIN 1250 1400

7698 BLAKE 2850

7839 KING 5000

7844 TURNER 1500 0

7986 STERN 1500

© Ellis Cohen 2002-2005 26

Object TablesObject-Relational Databases actually allow rows to be objects (known as row objects), and allow cells to contain references to these row objects.– Referential Integrity constraints can be

replaced by actual references– Joins can be replaced by Navigation– Instead of automatically associating an

extent with an object, an object is explicitly stored in some table (multiple tables can hold the same type of object)

– Every row object has an OID (invisibly provided by the database)

© Ellis Cohen 2002-2005 27

Object Types & Tables

CREATE TYPE DeptObj AS OBJECT ( deptno number(3), dname varchar(20), loc varchar(15),… )

CREATE TABLE DeptTable OF DeptObj (deptno PRIMARY KEY);

DeptTable can be viewed as either • a table containing 3 columns: deptno, dname, loc• a table containing a single column: a DeptObj

* SQL Syntax loosely based on Oracle

© Ellis Cohen 2002-2005 28

Returning Column Valuesfrom Object Tables

SELECT d.dname FROM DeptTable dWHERE d.loc = 'HOUSTON'– returns the department names

SELECT d.* FROM DeptTable dWHERE d.loc = 'HOUSTON'– returns a row (just as from an ordinary table)

30 SALES NY

10 ACCOUNTING LA

50 SUPPORT HOUSTON

99 PARTY MIAMI

© Ellis Cohen 2002-2005 29

Returning Column Values vs. ObjectsSELECT d.* FROM DeptTable d

WHERE d.loc = 'HOUSTON'– returns rows of values (just as from an ordinary table)

30 SALES NY

10 ACCOUNTING LA

50 SUPPORT HOUSTON

99 PARTY MIAMI

SELECT d FROM DeptTable dWHERE d.loc = 'HOUSTON'– returns entire DeptObj objects!

30 SALES NY

10 ACCOUNTING LA

50 SUPPORT HOUSTON

99 PARTY MIAMI

A DeptObj Object

© Ellis Cohen 2002-2005 30

Row Objects Have OIDs

27 622 Auditing CHICAGO …

deptno dname loc …

A row object's OID can be represented as a ROWID + a generation #, which also

appears in the row object's header

AAAGDxAABAAAH9EAAD27

© Ellis Cohen 2002-2005 31

Object ViewsCREATE TABLE Depts (

deptno number( 5 ),dname varchar( 30 ),loc varchar(30) )

Given an existing table, create an object view of it,but requires OID for each tuple

CREATE TYPE DeptObj AS OBJECT (deptno number( 5 ),dname varchar( 30 ),loc varchar(30) )

CREATE VIEW DeptView OF DeptObjWITH OBJECT OID (deptno) ASSELECT * FROM Depts

Note: No objects really exist or are created, so even though DeptView looks like a table of objects, the OID is just (id of Depts) + deptno, which is better than the ROWID (which can be reused) if deptno's are not changed or reused.

© Ellis Cohen 2002-2005 32

Type InheritanceCREATE TYPE EmpObj UNDER PersonObj (

empno number(4),…… )

CREATE TABLE PersonTable OF PersonObj

PersonTable can hold plain PersonObjs

as well as EmpObjs & other subclasses

ssno name addr

202406129 ALLEN 20 B St, … empno sal

… JONES … 1427 2500

… CHU … University

… SONI … Myanard Wales Univ

… HALMA …

… BONI … empno sal

… STERN … 6041 3300

EmpObj

GradObj

EmpObj

PersonObj

© Ellis Cohen 2002-2005 33

Type Checking & Casting

Suppose we want to get the empno's of all the employees in PersonTable

SELECT p.empnoFROM PersonTable pWHERE p IS OF TYPE EmpObj

Almost works, except we also need to claim that p is an EmpObj rather than just a PersonObj before getting its empno attribute

SELECT TREAT(p AS EmpObj).empnoFROM PersonTable pWHERE p IS OF TYPE EmpObj

© Ellis Cohen 2002-2005 34

Referenced Objects& Navigation

© Ellis Cohen 2002-2005 35

Object References

A column can contain a reference to a row object

30 SALES …

10 ACCOUNTING …

50 SUPPORT …

99 PARTY …

deptno dname loc

DeptTableempno name … dept

7499 ALLEN ...

7654 MARTIN …

7698 BLAKE …

7839 KING …

7844 TURNER …

7986 STERN …

EmpTable

© Ellis Cohen 2002-2005 36

Scoped ReferencesCREATE TYPE EmpObj AS OBJECT (

empno number(4), name varchar(30), …dept REF DeptObj SCOPE DeptTable )

– replaces the referential integrity constraint deptno number(3) REFERENCES DeptTable

CREATE TABLE EmpTable OF EmpObj(PRIMARY KEY empno)

REF(obj) creates a reference to the specified object, which can then be returned in a result set

UPDATE EmpTableSET dept = (SELECT REF(d) FROM DeptTable d WHERE d.dname = 'ACCOUNTING')WHERE name = 'SMITH'

This attribute holds a reference to a

DeptObj in DeptTable

Change SMITH's dept to ACCOUNTING

© Ellis Cohen 2002-2005 37

Comparing Queries

In a vanilla RDB, to find the department name in which JONES works, you might do

SELECT dnameFROM Emps NATURAL JOIN DeptsWHERE ename = 'JONES'

In an ORDB using EmpObj (which contains a REF DeptObj)

how would you get the dept name in which JONES works?

(Assume only one employee named JONES)

© Ellis Cohen 2002-2005 38

ORDBs Use Direct Navigation

CREATE TYPE EmpObj AS OBJECT ( empno number(4),name varchar(30),…,dept REF DeptObj SCOPE DeptObj

)

CREATE TABLE EmpTable OF EmpObj(PRIMARY KEY empno)

SELECT e. name, e.dept.dnameFROM EmpTable eWHERE ename = 'JONES'

List the names of employees whose departments are located in Denver.

© Ellis Cohen 2002-2005 39

Simple Query Solution

List the names of employees whose departments are located in Denver.

SELECT e.nameFROM EmpTable eWHERE e.dept.loc = 'DENVER'

© Ellis Cohen 2002-2005 40

Tables vs ExtentsObject types do not have a single

associated extentThere can be multiple tables which hold

objects of the same type

CREATE TABLE DeptTable1 OF DeptObj (deptno PRIMARY KEY);



The user chooses where to store an objectINSERT INTO DeptTable2

VALUES ( 50, 'SUPPORT', 'HOUSTON' );

Less signficant issue for DB's which support partitioned tables

© Ellis Cohen 2002-2005 41

Unscoped ReferencesCREATE TYPE EmpObj AS OBJECT (

empno number(4),name varchar(30),…dept REF DeptObj SCOPE DeptTable

)

CREATE TYPE EmpObj AS OBJECT (empno number(4),name varchar(30),…dept REF DeptObj

)

This DeptObj could be located in any table.

Must use a full-size OID to represent the reference

This DeptObj must be located in DeptTable.Could use a table-relative mini-OID

to represent the reference

© Ellis Cohen 2002-2005 42

Dereferencing Unscoped References

Even if departments are spread across multiple tables, an unscoped reference will find the department(by its OID!)

SELECT e.dept.dnameFROM EmpTable eWHERE e.ename = 'JONES'

Suppose in a vanilla RDB, depts were spread across Depts1, Depts2 & Depts3.

How would you get the name of the department in which JONES works?

© Ellis Cohen 2002-2005 43

Unions for Multi-Table NavigationSuppose in a vanilla RDB, depts were spread across

Depts1, Depts2 & Depts3. How would you get the name of the department in which JONES works?

SELECT dnameFROM Emps NATURAL JOIN Depts1WHERE ename = 'JONES'

UNIONSELECT dname

FROM Emps NATURAL JOIN Depts2WHERE ename = 'JONES'

UNIONSELECT dname

FROM Emps NATURAL JOIN Depts3WHERE ename = 'JONES';

In practice, tables are split for many reasonsdifferent divisions; pending vs active vs inactive, etc.

Using an Object Model with unscoped references allows simple navigation to replace unioned joins

© Ellis Cohen 2002-2005 44

DELETE & Dangling ReferencesDELETE deletes objects from tables of objects

Scoped References:provide referential integrity checking:– Can't delete referenced department (default)– ON DELETE SET NULL– ON DELETE CASCADE

Unscoped References:no referential integrity checking

– If a DeptObj is deleted,a REF DeptObj may hold an invalid OID (a dangling reference)

– Use IS DANGLING to check:

SELECT DISTINCT e.dept.dnameFROM EmpTable eWHERE e.job = 'SALESMAN' AND e.dept IS NOT DANGLING

© Ellis Cohen 2002-2005 45

Explicit DereferencingIf e denotes an EmpObj

then e.namedenotes the name attribute of that EmpObj

If re denotes a REF EmpObjthen DEREF(re)

denotes the EmpObj it references

and either DEREF(re).nameor re.namedenotes the name attribute of the EmpObj it references

© Ellis Cohen 2002-2005 46

Contained Objects

© Ellis Cohen 2002-2005 47

ContainmentORDB's are non-1NF:

Cells may contain objects as well as primitive types of values. These are also called cell objects or column objects.

CREATE TYPE Address AS OBJECT( street varchar(100), city varchar(40), state char(2), zip char(5))

CREATE TYPE PersonObj AS OBJECT(name varchar(30),addr Address

)CREATE TABLE PersonTable OF PersonObj

© Ellis Cohen 2002-2005 48

Cell Objects

SMITH

JONES

GOMEZ

SONI

name addr

… … MA 02139

… … IL 51320

… … CA 93710

… … MA 02445

p p.name p.addr p.addr.state

© Ellis Cohen 2002-2005 49

Creating Cell Objects

INSERT INTO PersonTableVALUES ( 'STERN', Address(

'11 Global Way', 'Hereville', MS, 39452 ) )

Cell Objects do not have OIDsREFs to Cell Objects are not allowed

© Ellis Cohen 2002-2005 50

Object Type Methods

CREATE TYPE AddrObj AS OBJECT (street varchar(100),city varchar(40),state char(2),zip char(5),

MEMBER FUNCTION toString RETURN varchar …

)

CREATE TYPE PersonObj AS OBJECT(name varchar(30),addr Address


SELECT name, addr.toString()FROM PersonTable

© Ellis Cohen 2002-2005 51

Ordering by Object TypesSELECT name FROM PersonTable

ORDER BY addr

How is an order defined on addresses?Oracle (e.g.) allows a single MAP member function

to be defined for AddrObjs. It returns a primitive type,

used as the basis of ordering

MAP MEMBER FUNCTION getZip RETURN char(5)IS RETURN zip;END

Oracle instead allows the ORDER member function;it compare two objects, returning-1 if the first is smaller 0 if they are equal 1 if the first is larger

Order AddrObjs based on their

zip values

© Ellis Cohen 2002-2005 52

Selecting with Member Functions

CREATE TABLE Positions( posid int, – id of the position coord Coordinate, – location of the position … )

SELECT posid FROM PositionsWHERE coord.inRegion( 0, 0, 100, 100) > 0

CREATE TYPE Coordinate AS OBJECT x number, y number, MEMBER FUNCTION inRegion RETURN INT … – returns 1 if coordinate is within the

specified region …)

© Ellis Cohen 2002-2005 53

Type-Specific Indexing

ORDB databases generally support type-specific indices

InRegion queries can be implemented as the intersection of x and y range queries based on B-tree indices, however

Coordinate-specific indices such as quadtree and R-tree indices select inRegion tuples much more quickly

© Ellis Cohen 2002-2005 55

Nested Tables

23 HR NY

31 SALES LA

… … … …

deptno dname loc empls

3049 SMITH … …

6471 JONES … …

8187 GOMEZ … …

2069 SONI … …

8142 EMEBI … …

Purist approaches to ORDB's (e.g. Date) only allows Nested Tables (and other Contained Objects and Collections), but do NOT allow Row Objects and References.

© Ellis Cohen 2002-2005 56

Nested Tables of ObjectsCREATE TYPE DeptEmpsObj As OBJECT (

deptno number(4),dname varchar(30),loc varchar(30),empls TABLE OF EmpObj

)CREATE TABLE DeptEmpsTable OF DeptEmpsObj

PRIMARY KEY deptno

SELECT dname FROM DeptEmpsTable dWHERE EXISTS( SELECT * FROM d.empls e WHERE e.job = 'SALESMAN')

SELECT e.name FROMDeptEmpsTable d, d.empls eWHERE d.loc = 'BOSTON'

List names of depts which have salesmen

List employees of depts located in Boston

Correlated table

expressions allowed on

nested tables

Now, of those employees,

determine how many have each

kind of job

© Ellis Cohen 2002-2005 57

Correlation Grouping Solution

Of the employees in departments located in Boston, determine how many have each kind of job.

SELECT e.job, count(*)FROM DeptEmpsTable d, d.empls eWHERE d.loc = 'BOSTON'GROUP BY e.job

© Ellis Cohen 2002-2005 58

Nested Update Problem

Nested Tables can be very efficient for some operations

SELECT e.nameFROM DeptEmpsTable d, d.emplsWHERE d.loc = 'NY' AND e.job = 'ANALYST'

How do you add 100 to the salary of these employees?You must use views!

© Ellis Cohen 2002-2005 59

Nested Tables & Unnested Views

23 HR NY

31 SALES LA

… … … …

deptno dname loc empls

3049 SMITH … …

6471 JONES … …

8187 GOMEZ … …

2069 SONI … …

8142 EMEBI … …

23 HR NY 3049 SMITH … …

23 HR NY 6471 JONES … …

23 HR NY 8187 GOMEZ … …

31 SALES LA 2069 SONI … …

… … … … …

deptno dname loc DeptEmpView

DeptEmpsTable

© Ellis Cohen 2002-2005 60

Views for UpdatingCREATE VIEW DeptEmpView AS

SELECT d.deptno, d.name, d.loc, e.*FROM DeptEmpsTable d, d.empls e

UPDATE DeptEmpViewSET sal = sal + 100 WHERE loc = 'NY' AND job = 'ANALYST'

Can we update deptno?

UPDATE DeptEmpView SET deptno = 31 WHERE empno = 6471

Updating deptno means moving the employee from one nested table to another. Might be supported in an ORDB

system, but perhaps it would be better for Emps & Depts to be the actual tables, and to create a nested table view

© Ellis Cohen 2002-2005 61

Result Sets with Nested TablesGiven Depts (only dept info) and Emps (only

employee info, except that Emps.deptno references Depts)

Generate a result set: each tuple corresponds to each of the departments – it contains the name of the department, and a table of the names of each employee in the department.

SELECT d.dname, TABLE( SELECT ename FROM Emps e WHERE e.deptno = d.deptno )FROM Depts d

Given Depts and Emps, create a view that corresponds to DeptEmpsTable (with its nested table of employees)

© Ellis Cohen 2002-2005 62

Creating Nested Table Views

CREATE VIEW DeptEmpsTableView OF DeptObjWITH OBJECT OID (deptno) ASSELECT d.*, TABLE( SELECT empno, … FROM Emps e WHERE d.deptno = e.deptno) AS emplsFROM Depts d

Oracle also allows definition of the original DeptEmpsTable, with the combined nested tables of all the Employees

implemented as a single query-able table

Given Depts and Emps, create a view that corresponds to DeptEmpsTable (with its nested table of employees)

© Ellis Cohen 2002-2005 63

Nested Result Sets from References

Generate a result set: each tuple contains a department name and a table of the names of the dept employees

30 SALES …

10 ACCOUNTING …

50 SUPPORT …

99 PARTY …

deptno dname loc


7499 ALLEN ...

7654 MARTIN …

7698 BLAKE …

7839 KING …

7844 TURNER …

7986 STERN …

EmpTable

© Ellis Cohen 2002-2005 64

Result Set Solution

SELECT d.dname, TABLE( SELECT name FROM EmpTable e WHERE e.dept = REF(d) )FROM DeptTable d

Generate a result set: each tuple contains a department name and a table of the names of the dept employees

Generate the same result set, but givenDeptEmpsTable (each dept has empls, a nested table of employees)

© Ellis Cohen 2002-2005 65

Related Nested Result Set

SELECT d.dname, TABLE( SELECT name FROM d.empls )FROM DeptEmpsTable d

Notice that SELECT d.dname, d.empls.name

FROM DeptEmpsTable dis incorrect!

Generate a result set: each tuple contains a department name and a table of the names of the dept employees, given DeptEmpsTable

© Ellis Cohen 2002-2005 66

Cross Referencing

30 SALES

10 ACCOUNTING

50 SUPPORT

deptno dname empls


7499 ALLEN ...

7654 MARTIN …

7698 BLAKE …

7839 KING …

7844 TURNER …

7986 STERN …

EmpTable

Suppose we keep the employees in a separate table

And every department contains a table containing just references to the employees in that department

© Ellis Cohen 2002-2005 67

Nested Tables of RefsCREATE TYPE RefEmp AS REF EmpObj SCOPE EmpTable;

CREATE TYPE DeptObj AS OBJECT (deptno number(4),dname varchar(30),loc varchar(30),empls TABLE OF RefEmp

)CREATE TABLE DeptTable OF DeptObj

PRIMARY KEY deptno

SELECT dname FROM DeptTable dWHERE EXISTS( SELECT * FROM d.empls e WHERE e.job = 'SALESMAN')

SELECT e.name FROMDeptTable d, d.empls eWHERE d.loc = 'Boston'

© Ellis Cohen 2002-2005 68

ODL Modelclass Employee (extent emps) {

attribute int empno;attribute string name;attribute string job;attribute Address addr;relationship Dept dept inverse Dept::empls;

}

class Dept (extent depts) {attribute int deptno;attribute string dname;relationship Set<Employee> empls

inverse Employee::dept;

The ODL model for Employee and Dept is essentially equivalent to the previous ORDB model

• emps and depts correspond to EmpTable and DeptTable• Set<Employee> empls corresponds to a nested tables of refs

© Ellis Cohen 2002-2005 69

Collections and Relationships

deptsemps

dept1

dept2

dept3

emp1

emp3

emp5

emp4

emp2

empls

dept

© Ellis Cohen 2002-2005 71

Collection Types

ORDB's may support other collection types

SET OF TypBAG OF TypLIST OF TypARRAY[n] OF TypDICTIONARY[ndxtyp] OF Typ

They can– Be placed in cells

These are useful because– there are specialized functions & operations to

add/remove/get/set/test values

Oracle supports VARRAYS, resizeable

arrays with a fixed maximum size

© Ellis Cohen 2002-2005 72

Collections & MembershipIt may be possible to test collections for

membership

CREATE TYPE PersonObj AS OBJECT (name varchar(30),kidnames SET OF varchar(30)


List the names of the people who have a kid named 'Yael'

SELECT name FROM PersonTablewhere ('Yael' IN kidnames)

© Ellis Cohen 2002-2005 73

Collection OperationsIt may be possible to use specialized

collection operations

CREATE TYPE PersonObj AS OBJECT (name varchar(30),autos LIST OF AutoObj


List each person and the model of their primary car

SELECT name, autos[1].model FROM PersonTable

© Ellis Cohen 2002-2005 74

Querying CollectionsGenerally, collections cannot be queriedIt may be possible to convert collections to tables

in order to query them

CREATE TYPE PersonObj AS OBJECT (name varchar(30),autos LIST OF AutoObj


List the model, year & owner of all autos made before 1950.Order by model and year

SELECT a.model, a.year, p.name FROM PersonTable p, TABLE(p.autos) aWHERE a.year < 1950ORDER BY a.model, a.year

© Ellis Cohen 2002-2005 75

Collection ConversionsIt may be possible to convert

tables or collections to other collectionsso collection-specific operations may be used

CREATE TYPE PersonObj AS OBJECT (name varchar(30),autos TABLE OF AutoObj

)

SELECT name, LIST(autos ORDER BY position DESC)[1].model FROM PersonTable

List each person and the model of their primary car

1 advanced database topics copyright © ellis cohen 2002-2005 objects and relational databases these...

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