Seminar 10a : OODB Design

1
Seminar 10a OODB Design

• Purpose
• This seminar is the continuation of seminar 6.
• How different UML associations are implemented in
  ODL.
• 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.
• 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).
• 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 and also
  where unsigned short may be the ideal choice as
  lambda-DB complaints about unsigned short when
  used as attribute.
• 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 cgapp1 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.
• If completed Seminar 6 (last week) then carry on
  with the tasks of this seminar (by editing
  seminar6.odl to add relationships).
• Otherwise run the script for setting up seminar7a
  files by
• /home/makhtarali/CM036/setupSem7
• The solution of Seminar 6 is available online.
• Go to the folder seminar 7a by cd CM036/seminar7
• Open the file seminar7.odl and complete the
  schema by
• pico seminar7.odl. Save by Ctrl x.
• Once ready, compile the schema by make (note if
  you were not in last week or you did not run
  make build before, then run make build before you
  compile schema by make)
• If the compiler reports errors open seminar7.odl
  and go to the specific line by Ctrl w then
  Ctrl t.
• Save and recompile (by make) until all errors are
  removed.

8
Tasks for the Seminar

• It is assumed that you have either completed
  seminar 6 or you have copied the files of seminar
  10 to start with.
• Using the implementation of different kinds of
  associations in ODL (described in the Lecture
  10), implement the various associations given in
  Figure 1 using ODL.