Data Dictionary. Relational Schema Diagram

1. Advance Database Systems
Overview of Data Modeling

2. Contents
• Data Dictionary
• Relational Schema Diagram

3. Data Dictionary
• A data dictionary is a collection of descriptions of the data objects or
items in a data model for the benefit of programmers and others who
need to refer to them.

4. Relational Schema Diagram
• A relational schema diagram is
the skeleton structure that
represents the conceptual
view(transformed ERD) of the
entire database.
• It defines how the data is
organized and how the relations
among them are associated.
• It expresses about the
constraints/checks that are to be
applied on the data.

5. ERD Reading

7. Logical Data Modeling/Transformation into
Relations (Tables)
Relation
• Rows or Record or Tuples or
Instances of an ENTITY
• Columns or Fields or Labels or
Attributes in ERD
• Keys (Primary and Foreign Keys)
• Constraints / Restrictions /
Limitations/ Check

8. Rows or Record or Tuples or Instances of an ENTITY
• A record contains all the information about a single ‘member’ of a
table.
• It is a collection of attributes values.
• Records are also known as tuples.

9. Relation (Table)
• A relation is a named, two-dimensional table of data. A Table consists of rows
(tuples or records) and columns (attributes or fields)
Requirements for a table to qualify as a relation
• Table must have a Unique Name in same Database
• Primary Key must be assigned; each record must be uniquely identified
• There are no repeating groups: two columns do not store similar information in
the same table
• Every attribute value must be atomic (no multivalued attributes are allowed)
• Every Record in row must store unique values (can’t have two rows with exactly
the same values against all their fields/columns)
• Attributes (columns) in tables must have unique names
• The order of the columns can be irrelevant/un-ordered
• The order of the rows can be irrelevant/un-ordered

10. Key Fields
• Keys are special fields that serve two main purposes:
• Primary keys are Unique Identifiers of the relation(table) with not
null constraint/check/limitation. Examples include person Cnic
Number. This is how we can guarantee that all rows(tuples/record)
are unique and having some value against the attribute.
• Foreign keys are attribute in a relation (table) of a database that
serves in a child relation (table) connecting parent relation (table) in
the same database.
• Keys can be simple(a single field) or composite(more than one fields)
• Keys usually are used as Indexes to speed up the response to user
queries

11. (Primary Key)
(Foreign Key)
(Combined, these are a
composite primary key)

13. Integrity Constraints/Limitations/Check/Restrictions
1) Domain Constraints:
• Allowable values for an Attribute (Data Type of a
Label/Column/Attribute). See Table 5-1 on next slide.
2) Entity Integrity:
• No primary key attribute have null value. All primary key fields must
contain Unique data.

14. 3) Referential Integrity:
• This rule states that any foreign key value(on the relation/table of the many
side) MUST match a primary key value in the relation/table of the one side
in one_to_many type of relationship. (Foreign key may store a null value
but not Primary key)
• For example: Update/Delete/Restrict Rules
• Restrict: don’t allow update or delete of parent side records(P.K) if related
records that exists independent side/child table(F.K)
• Cascade: automatically update or delete dependent side/child table
records(F.K) that relates with the parent side records(P.K)
• Set-to-Null: the foreign key (F.K) in the dependent side set to null if
deleting from the parent side (P.K)

15. SQL table definitions
Referential
integrity
constraints are
implemented
with foreign key
to primary key
references

17. Well Structured Relation :

18. Insertion Anomaly/Irregularity/Inconsistency:
• Suppose that we need to add a new employee to the table shown in
next slide. The primary key for this relation is the combination of
Emp_ID and Course_Title. There fore, to insert a new record, the user
must supply values for both Emp_ID and Course_Title(because
primary key values can not be null or non existent). This is an
anomaly. Because the user should not be able to enter only employee
data without supplying course data.

19. Example of an Insertion, Deletion & Modification Anomaly/Irregularity/Inconsistency

20. EMPLOYEE_to_COURSE:
• An EMPLOYEE must studies at least one COURSE. A COURSE must be
studied by one or more than one EMPLOYEE's(MANY_to_MANY type
of Relationship).

21. EMPLOYEE_to_DEPARTMENT:
• An EMPLOYEE must do his/her job in at most one DEPARTMENT. In a
DEPARTMENT at most one EMPLOYEE must do his/her
job(ONE_to_ONE type of Relationship).

23. Transforming/Mapping ENTITIES into Relations
(Tables)
• Mapping Regular Entities to Relations
1.Simple Attributes: E-R attributes map directly onto the relation
2.Composite Attributes: Use only their simple, component attributes
3.Multivalued Attribute: Becomes a separate relation with a foreign
key taken from the superior entity.
Mapping a Regular Entity
(a) CUSTOMER entity type with
simple attributes
(b) CUSTOMER Relation

24. (b) CUSTOMER relation
with address detail
(a) CUSTOMER entity type
with composite attribute

25. Removing Multivalued Attributes from Tables

26. a) Table with Repeating Groups:
EMPLOYEE 2 Relation:

27. Mapping an Entity with a Multivalued Attribute
• Multivalued attribute becomes a separate relation with foreign key
• One–to–Many relationship between original entity and new relation

28. Mapping Weak Entities into Relation (Tables)
• Becomes a separate relation with a foreign key taken from the
superior entity
Primary Key composed of:
• Primary Key of identifying relation (Strong Entity)
Example of Mapping a Weak Entity

29. Strong and Weak Entity Type Symbol of
Representation

30. Transforming/Mapping Unary Relationship into
Relations (Tables)
• One-to-Many–Recursive foreign key in the same relation
• Many-to-Many–Two relations:
• One for the entity type
• One for an associative relation in which the primary key has two
attributes, both taken from the primary key of the entity
• Mapping a unary 1:N relationship
(b) EMPLOYEE relation
with recursive foreign key
(a) EMPLOYEE entity
with unary relationship

31. Mapping a unary M:N relationship
(a) Bill-of-materials
relationships (M:N):
(b) ITEM and
COMPONENT
relations

32. Transforming/Mapping Binary Relationship
into Relations (Tables)
• One-to-Many:
• Primary key on the one side becomes a foreign key on the many side.
• Many-to-Many:
• Create a new relation named as Associative/Junction Table with the
primary keys of the two entities as its primary key in Binary Degree of
Relationship.
• One-to-One:
• Primary key on the Strong/Independent side becomes a foreign key
on the Weak/Dependent side.

33. Transforming/Mapping Ternary Relationship
into Relations (Tables)
• One relation for each entity and one for the Associative entity
• Associative/Junction entity has foreign keys to each entity in the
relationship