1. 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)

2. Conceptual model for Company database
Figure 1
Seminar #: 6 (Object Oriented Database Schema in ODL) Advanced Databases (CM036)

3. Company Relational DB Schema
Figure 2
Seminar #: 6 (Object Oriented Database Schema in ODL) Advanced Databases (CM036)

4. 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)

5. 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)

6. 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)

7. 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)

8. 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)

9. Sample Company Database (relational)
Figure 3
Seminar #: 6 (Object Oriented Database Schema in ODL) Advanced Databases (CM036)