The document discusses the entity-relationship (E-R) data model. It was proposed by Dr. Peter Chen and represents data graphically using entity sets, attributes, and relationships. Entity sets are collections of abstract objects, attributes are concrete data used to define entity sets, and relationships specify connections between entity sets. The E-R model uses a diagram with rectangles for entity sets, ovals for attributes, and diamonds for relationships. It allows modeling of one-to-one, many-to-one, and many-to-many connections between entity sets. The model aims to faithfully represent specifications simply without redundancy.

1. Entity-Relationship Data
Model
Alex Ostrovsky

2. Presentation Overview
►Short historical overview
►Elements of E-R Model
►Basic organization & relationships in E-R
Model
►Design principles

3. History of E-R Model
► E-R Model was proposed
by Dr. Peter Chen
(currently professor at
Louisiana State
University)
► Chen’s original paper on
E-R Model is the 35th
most sited paper in
computer science
► Chen has written papers
interconnecting E-R
model and linguistics

4. Introduction
►Database Structure is often called Database
Schema
►E-R model is graphical in nature, thus
making it easy to analyze and observe
relationship between data elements
►Most DBMS are based upon E-R model
►E-R model is not a good match for the
sophisticated data structures required in
today’s DBMS

5. Elements of E-R Model
►Data represented graphically via entity-
relationship diagram which contains 3 main
element types:
 Entity sets
 Attributes
 Relationships

6. Entity sets, Attributes, Relationships
► Entity set
 Is an abstract object, collection of such objects forms
an entity set.
 Similar notion as in OO design
► Attribute:
 Some concrete data (or object type) by which entity set
is defined
► Relationship
 Specific connection between 2 or more entity sets

7. E-R Diagram
►Represents E-R elements by nodes of
specific shape to indicate kind
 Entity sets are represented by rectangles
 Attributes are shown as ovals
 Relationships correspond to diamonds
►Simple example from the book:

8. Simple illustration

9. Instances of E-R diagram
►DB described by E-R will contain specific
data (i.e. database instance)
►Each entity set will contain a particular finite
set of entities
►Each entity contains a particular value for
each attribute
►E-R data is not stored directly in DB

10. E-R Relationships
► Suppose R is a relationship connecting entity sets
E and F. Then:
 If each member of E can be connected by R to at
most one member of F, then we say that R is many-
one from E to F. Note that in a many-one relationship
from E to F, each entity in F can be connected to many
members of E.
 If R is both many-one from E to F and many-one from F
to E, then we say that R is one-one. In a one-one
relationship an entity of either entity set can be
connected to at most one entity of the other set.
 If R is neither many-one from E to F or from F to E,
then we say R is many-many

11. Multi-way relationships
► There is a relationship Sequel-of between the entity set
Movies and itself.
► To differentiate the two movies in a relationship, one line
is labeled by the role Original and one by the role Sequel,
indicating the original movie and its sequel, respectively.

12. Relationships Continued
►Some data models limit relationships to be
binary
►It is possible to convert multi-way
relationship into a collection of binary many-
one relationships
►Need to introduce a connecting entity set,
which will act as a bridge between smaller
sets which come from splitting a larger
multi-way relationship set.
►Connecting entity set might have its own
attributes

13. Design Principles
► Faithfulness:
 Design has to comply strictly with specifications
 Logical attributes and relationships
► Avoid redundancy
► "Everything should be made as simple as possible,
but not simpler.” Albert Einstein
► Choose right relationships
► Select right elements
 Many choices exist between using attributes and using
entity set/relationship combinations
 An attribute is simpler to implement than either entity
set or a relationship

14. Design Principals Cont.
►To replace an entity set by an attribute or
attributes of several entity sets 3 conditions
must be enforced:
 All relationships in which entity set is involved
must have arrows entering it. That is, it must be
the “one” in many-one relationships, or its
generalization for the case of multi-way
relationships.
 The attributes for E must collectively identify an
entity. if there are several attributes, then no
attribute must depend on the other attributes
 No relationship involves E more than once

15. Thank You.