Seminar 6 : OODB Schema in ODL

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 employees
  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.

2
Conceptual model for Company database
Figure 1
3
Company Relational DB Schema
Figure 2
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).

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, setltDependentgt, etc).

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

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.

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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.

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Sample Company Database (relational)
Figure 3