Transcript Seminar 5: OO Database Design

Seminar 6 : OODB Schema in ODL

Purpose




To understand how an OODB is structured.
How a class diagram in UML is mapped onto an ODL schema.
How a relational mapping of a UML class diagram can be compared with
an object-oriented representation.
Scenario





A UML class diagram of a Company database is given in Figure 1, which
shows a conceptual model of the database.
Company database models the data for a company that has several
departments, many employees work for departments on different projects.
The database also stores data on employee’s dependents.
A mapping of the conceptual model into relational model is given in Figure
2 and a sample relational database shown in Figure 3 (at the end of
handout).
It is assumed that the students understand UML notations and are familiar
with relational concepts.
Seminar #: 6 (Object Oriented Database Schema in ODL) Advanced Databases (CM036)
1
Conceptual model for Company database
Figure 1
Seminar #: 6 (Object Oriented Database Schema in ODL) Advanced Databases (CM036)
2
Company Relational DB Schema
Figure 2
Seminar #: 6 (Object Oriented Database Schema in ODL) Advanced Databases (CM036)
3
Relational Schema





Relationships are implemented using foreign keys. See arrows ( )
from foreign keys to the primary keys.
Many-to-many relationships are implemented as a linking relation
using primary keys of participating relations (see WORKS_ON
relation).
The real-world concept that an instance of one entity is associated
with one or many instances of another entity is not present in
relational model. For example, the concept that a department has
many employees working for it is not present in the model. The only
thing that exist is that an employee has an extra attribute (DNO) that
holds the primary key value of his/her department.
Multi-valued attributes are implemented as a separate relation (e.g.,
DEPT_LOCATIONS).
Composite attributes (e.g. Name) is implemented in terms of its
components (e.g., Fname, Minit, Lname).
Seminar #: 6 (Object Oriented Database Schema in ODL) Advanced Databases (CM036)
4
Object Oriented Database Design

Fundamental Principles






All kinds of relationships are implemented directly using either single
valued or multi-valued attributes in both participating entities (classes).
This aspect of the design will be addressed in next lecture/seminar.
Multi-valued attributes are implemented as collection valued attributes
(e.g., set, bag, list).
Composite attributes are implemented directly (i.e., struct).
Primary keys are not required but supported for their usefulness in
query processing.
Value-based foreign keys are not present ODBs.
The data type of attributes can be primitive (e.g., short, float, string,
etc) as well as constructed types and collections (e.g., Department,
Employee, set<Dependent>, etc).
Seminar #: 6 (Object Oriented Database Schema in ODL) Advanced Databases (CM036)
5
Using ODL


Use short data type for int or integer.
Follow these guidelines when using ODL with lambda-DB
due to some limitations:



Use short data type for operations that return boolean or
unsigned short.
Use string data type where char applies.
Define a composite literal type (using struct) and use it where
date applies. For example, if you are going to define an attribute:
attribute date birthDate;
then define date_type as a literal (i.e., struct) first and then
write:
attribute date_type birthDate;
Seminar #: 6 (Object Oriented Database Schema in ODL) Advanced Databases (CM036)
6
Using Lambda-DB








Open a DOS window.
Connect to cgapp2 using your Unix user account and password by
writing
telnet cgapp2 on the Linux prompt.
From now on every thing you type is case-sensitive.
Run the script for setting up seminar6 files by
/home/makhtarali/CM036/setupSem6
Go to the folder seminar6 by cd CM036/seminar6
Open the file seminar6.odl and complete the schema by
pico seminar6.odl. Save by Ctrl + x.
Once ready, compile the schema by make build and make
If the compiler reports errors open seminar6.odl and go to the
specific line by Ctrl + w then Ctrl + t. Save and recompile (by make)
until all errors are removed.
Seminar #: 6 (Object Oriented Database Schema in ODL) Advanced Databases (CM036)
7
Tasks for the Seminar



It is assumed that you understand what the UML
notations stand for and how they are mapped onto
relational model. The UML conceptual model is provided
to give you an idea of how the relational model came into
existence in the first place.
Complete implementation of the UML class diagram as
an OO schema using ODL. A start-up schema
(seminar6.odl) is available from blackboard and on the
Linux server. Concentrate on representing classes with
their attributes and operations. Leave associations and
association classes for the next seminar.
Implementation of the UNN_IS1 schema in ODL is given
for your guidance and is available from blackboard.
Seminar #: 6 (Object Oriented Database Schema in ODL) Advanced Databases (CM036)
8
Sample Company Database (relational)
Figure 3
Seminar #: 6 (Object Oriented Database Schema in ODL) Advanced Databases (CM036)
9