it describes about Data Model Basic Building Blocks in Using High level Data Models for Database Design Entity types and Sets, Attributes and Keys, Relationships, Roles and Structural Constraints, Enhanced ER Diagram, E-R mapping to Relational Database model.
This presentation discusses the following topics:
Object Oriented Databases
Object Oriented Data Model(OODM)
Characteristics of Object oriented database
Object, Attributes and Identity
Object oriented methodologies
Benefit of object orientation in programming language
Object oriented model vs Entity Relationship model
Advantages of OODB over RDBMS
● Data Modeling and Data Models.
● Business Rules (Translating Business Rules into Data Model Components).
● Emerging Data Models: Big Data and NoSQL.
● Degrees of Data Abstraction (External, Conceptual, Internal and Physical model).
This presentation discusses the following topics:
Object Oriented Databases
Object Oriented Data Model(OODM)
Characteristics of Object oriented database
Object, Attributes and Identity
Object oriented methodologies
Benefit of object orientation in programming language
Object oriented model vs Entity Relationship model
Advantages of OODB over RDBMS
● Data Modeling and Data Models.
● Business Rules (Translating Business Rules into Data Model Components).
● Emerging Data Models: Big Data and NoSQL.
● Degrees of Data Abstraction (External, Conceptual, Internal and Physical model).
Database systems that were based on the object data model were known originally as object-oriented databases (OODBs).These are mainly used for complex objects
Introduction to Relational algebra in DBMS - The relational algebra is explained with all the operations. Some of the examples from the textbook is also solved and explained.
FellowBuddy.com is an innovative platform that brings students together to share notes, exam papers, study guides, project reports and presentation for upcoming exams.
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# Students can catch up on notes they missed because of an absence.
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Our Vision & Mission – Simplifying Students Life
Our Belief – “The great breakthrough in your life comes when you realize it, that you can learn anything you need to learn; to accomplish any goal that you have set for yourself. This means there are no limits on what you can be, have or do.”
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Database systems that were based on the object data model were known originally as object-oriented databases (OODBs).These are mainly used for complex objects
Introduction to Relational algebra in DBMS - The relational algebra is explained with all the operations. Some of the examples from the textbook is also solved and explained.
FellowBuddy.com is an innovative platform that brings students together to share notes, exam papers, study guides, project reports and presentation for upcoming exams.
We connect Students who have an understanding of course material with Students who need help.
Benefits:-
# Students can catch up on notes they missed because of an absence.
# Underachievers can find peer developed notes that break down lecture and study material in a way that they can understand
# Students can earn better grades, save time and study effectively
Our Vision & Mission – Simplifying Students Life
Our Belief – “The great breakthrough in your life comes when you realize it, that you can learn anything you need to learn; to accomplish any goal that you have set for yourself. This means there are no limits on what you can be, have or do.”
Like Us - https://www.facebook.com/FellowBuddycom
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Dive into the world of AI! Experts Jon Hill and Tareq Monaur will guide you through AI's role in enhancing nonprofit websites and basic marketing strategies, making it easy to understand and apply.
June 3, 2024 Anti-Semitism Letter Sent to MIT President Kornbluth and MIT Cor...Levi Shapiro
Letter from the Congress of the United States regarding Anti-Semitism sent June 3rd to MIT President Sally Kornbluth, MIT Corp Chair, Mark Gorenberg
Dear Dr. Kornbluth and Mr. Gorenberg,
The US House of Representatives is deeply concerned by ongoing and pervasive acts of antisemitic
harassment and intimidation at the Massachusetts Institute of Technology (MIT). Failing to act decisively to ensure a safe learning environment for all students would be a grave dereliction of your responsibilities as President of MIT and Chair of the MIT Corporation.
This Congress will not stand idly by and allow an environment hostile to Jewish students to persist. The House believes that your institution is in violation of Title VI of the Civil Rights Act, and the inability or
unwillingness to rectify this violation through action requires accountability.
Postsecondary education is a unique opportunity for students to learn and have their ideas and beliefs challenged. However, universities receiving hundreds of millions of federal funds annually have denied
students that opportunity and have been hijacked to become venues for the promotion of terrorism, antisemitic harassment and intimidation, unlawful encampments, and in some cases, assaults and riots.
The House of Representatives will not countenance the use of federal funds to indoctrinate students into hateful, antisemitic, anti-American supporters of terrorism. Investigations into campus antisemitism by the Committee on Education and the Workforce and the Committee on Ways and Means have been expanded into a Congress-wide probe across all relevant jurisdictions to address this national crisis. The undersigned Committees will conduct oversight into the use of federal funds at MIT and its learning environment under authorities granted to each Committee.
• The Committee on Education and the Workforce has been investigating your institution since December 7, 2023. The Committee has broad jurisdiction over postsecondary education, including its compliance with Title VI of the Civil Rights Act, campus safety concerns over disruptions to the learning environment, and the awarding of federal student aid under the Higher Education Act.
• The Committee on Oversight and Accountability is investigating the sources of funding and other support flowing to groups espousing pro-Hamas propaganda and engaged in antisemitic harassment and intimidation of students. The Committee on Oversight and Accountability is the principal oversight committee of the US House of Representatives and has broad authority to investigate “any matter” at “any time” under House Rule X.
• The Committee on Ways and Means has been investigating several universities since November 15, 2023, when the Committee held a hearing entitled From Ivory Towers to Dark Corners: Investigating the Nexus Between Antisemitism, Tax-Exempt Universities, and Terror Financing. The Committee followed the hearing with letters to those institutions on January 10, 202
The Roman Empire A Historical Colossus.pdfkaushalkr1407
The Roman Empire, a vast and enduring power, stands as one of history's most remarkable civilizations, leaving an indelible imprint on the world. It emerged from the Roman Republic, transitioning into an imperial powerhouse under the leadership of Augustus Caesar in 27 BCE. This transformation marked the beginning of an era defined by unprecedented territorial expansion, architectural marvels, and profound cultural influence.
The empire's roots lie in the city of Rome, founded, according to legend, by Romulus in 753 BCE. Over centuries, Rome evolved from a small settlement to a formidable republic, characterized by a complex political system with elected officials and checks on power. However, internal strife, class conflicts, and military ambitions paved the way for the end of the Republic. Julius Caesar’s dictatorship and subsequent assassination in 44 BCE created a power vacuum, leading to a civil war. Octavian, later Augustus, emerged victorious, heralding the Roman Empire’s birth.
Under Augustus, the empire experienced the Pax Romana, a 200-year period of relative peace and stability. Augustus reformed the military, established efficient administrative systems, and initiated grand construction projects. The empire's borders expanded, encompassing territories from Britain to Egypt and from Spain to the Euphrates. Roman legions, renowned for their discipline and engineering prowess, secured and maintained these vast territories, building roads, fortifications, and cities that facilitated control and integration.
The Roman Empire’s society was hierarchical, with a rigid class system. At the top were the patricians, wealthy elites who held significant political power. Below them were the plebeians, free citizens with limited political influence, and the vast numbers of slaves who formed the backbone of the economy. The family unit was central, governed by the paterfamilias, the male head who held absolute authority.
Culturally, the Romans were eclectic, absorbing and adapting elements from the civilizations they encountered, particularly the Greeks. Roman art, literature, and philosophy reflected this synthesis, creating a rich cultural tapestry. Latin, the Roman language, became the lingua franca of the Western world, influencing numerous modern languages.
Roman architecture and engineering achievements were monumental. They perfected the arch, vault, and dome, constructing enduring structures like the Colosseum, Pantheon, and aqueducts. These engineering marvels not only showcased Roman ingenuity but also served practical purposes, from public entertainment to water supply.
Honest Reviews of Tim Han LMA Course Program.pptxtimhan337
Personal development courses are widely available today, with each one promising life-changing outcomes. Tim Han’s Life Mastery Achievers (LMA) Course has drawn a lot of interest. In addition to offering my frank assessment of Success Insider’s LMA Course, this piece examines the course’s effects via a variety of Tim Han LMA course reviews and Success Insider comments.
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2024.06.01 Introducing a competency framework for languag learning materials ...Sandy Millin
http://sandymillin.wordpress.com/iateflwebinar2024
Published classroom materials form the basis of syllabuses, drive teacher professional development, and have a potentially huge influence on learners, teachers and education systems. All teachers also create their own materials, whether a few sentences on a blackboard, a highly-structured fully-realised online course, or anything in between. Despite this, the knowledge and skills needed to create effective language learning materials are rarely part of teacher training, and are mostly learnt by trial and error.
Knowledge and skills frameworks, generally called competency frameworks, for ELT teachers, trainers and managers have existed for a few years now. However, until I created one for my MA dissertation, there wasn’t one drawing together what we need to know and do to be able to effectively produce language learning materials.
This webinar will introduce you to my framework, highlighting the key competencies I identified from my research. It will also show how anybody involved in language teaching (any language, not just English!), teacher training, managing schools or developing language learning materials can benefit from using the framework.
chapter 3-Data Modelling using Entity Relationship .pdf
1. Fundamentals of Database
system
Chapter Three:
Data Modelling using
Entity Relationship Model
Prepared by:
Misganaw Abeje
University of Gondar
College Of Informatics
Department of computer science
Misganaw.Abeje13@gmail.com
2. Outline
Data Model Basic Building Blocks
Using High level Data Models for Database Design
Entity types and Sets, Attributes and Keys
Relationships, Roles and Structural Constraints
Weak Entity Types
Enhanced ER Diagram
E/R mapping to Relational
BY: MA
3. Data Model Basic Building Blocks
To design a database first we have to understand the
basic Building block of relational Data model.
Entity: anything about which data are to be collected and
stored
Attribute: a characteristic of an entity
Relationship: describes an association
among entities
– One-to-many (1:M) relationship
– Many-to-many (M:N or M:M) relationship
– One-to-one (1:1) relationship
• Constraint: a restriction placed on the data
BY: MA
4. Business Rules
Descriptions of policies, procedures, or principles within
a specific organization
– Apply to any organization that stores and uses data to
generate information
Description of operations to create/enforce actions
within an organization’s environment.
Must be in writing and kept up to date.
Must be easy to understand and widely disseminated.
Describe characteristics of data as viewed by the
company.
BY: MA
5. Discovering Business Rules
Sources of business rules:
– Company managers
– Policy makers
– Department managers
– Written documentation
Procedures
Standards
Operations manuals
– Direct interviews with end users
BY: MA
6. Cont…
Standardize company’s view of data
Communications tool between users and designers
Allow designer to understand the nature, role, and
scope of data.
Allow designer to understand business processes
Allow designer to develop appropriate relationship
participation rules and constraints .
BY: MA
7. Translating Business Rules into
Data Model Components
Generally:
nouns translate into entities
Verbs translate into relationships among entities.
possessive phrases or description of refers to
attribute of entities.
Relationships are bidirectional.
Two questions to identify the relationship type:
– How many instances of B are related to one
instance of A?
– How many instances of A are related to one
instance of B?
BY: MA
8. Using High level Data Models for Database Design
High-level conceptual data models provide concepts
for presenting data in ways that are close to the way
people perceive data.
A typical example is the entity relationship model, which
uses main concepts like entities, attributes and
relationships.
The two common conceptual models for Relational
Database system are
– Entity – Relationship (E/R) model
– Object-Oriented Data Language (ODL) model
BY: MA
9. Entity – Relationship (E/R) Data Model
The E/R data model views the real world as a
set of
– Basic objects (Entities), and
– Relationships among these objects.
The three basic notions of the E/R model are:
– Entity
– Relationship
– Attribute
BY: MA
10. Cont…
Entities are usually recognizable concepts, either
concrete or abstract, such as:
– person, places, things, or events which have
relevance to the database.
An Entity Set is then a set consisting of the same
type of entities that share same properties.
In the requirement analysis the entities are
recognized by nouns and noun phrases.
BY: MA
11. Cont…
Entities can be classified as:
– Strong (independent) entity
One that does not rely on other entities for identification.
– Weak (dependent) entity
one that relies on other entities for identification.
Instance
– Instance also known as Object is an individual
occurrence of an entity set.
BY: MA
12. Attributes
Attributes are descriptive properties that are
associated with an entity.
Value
– Value is a particular instance of an attribute.
Domain
– The domain of an attribute is the collection of all
possible values an attribute can have.
BY: MA
13. Classification of Attributes
Identifiers
– more commonly called keys, uniquely identify an
instance of an entity.
Descriptor
– describes a non-unique characteristic of an entity
instance.
Example
– furniture Id
– catalog number, model type, color, …
13
BY: MA
14. … Classification of Attributes
Simple Attributes
– also known as Atomic Attributes that can not be divided
into subparts mainly of primitive types.
Composite Attributes
– are composed of smaller subparts that can be further
subdivided into the subparts (Attributes).
Example
– Id, type, price, color
– name, address
14
BY: MA
15. … Classification of Attributes
Single-valued Attributes
– are attributes having only one possible value at any
time.
Multi-valued Attributes
– are attributes that are having possibly more than one
value.
Example
– Id, name, type, price
– Address, degree
15
BY: MA
16. … Classification of Attributes
Derived Attributes
– are attributes that can be calculated from the related
stored attributes, entities or general states.
Stored Attributes
– are attributes that can not be calculated in any way
from the stored attributes.
Example
– Age
– Birth Date
16
BY: MA
17. Relationship Sets
A Relationship represents an association between
two or more entities.
Example
– FURNITURE is produced by an EMPLOYEE from
RESOURCE
FURNITURE is produced by EMPLOYEE
FURNITURE is produced from RESOURCE
SALE of FURNITURE is made with RECEIPT
17
BY: MA
18. … Relationship Sets
A Relationship Set is then a set consisting same types of relationships. A
relationship should be named by a Verb or phrase which explains its
function (role name)
Classification terms in Relationships
1. Degree
– number of entities associated with the relationship
Binary – links two entity sets; set of ordered pairs (most common)
E.g. STUDENT and DORMITORY || STUDENT and COURSE
– Ternary – links three entity sets; ordered triples (rare). If a
relationship exists among the three entities, all three must be present.
E.g. INSTRUCTOR ,STUDENTS and a particular COURSE
N-ary – links n entity sets; ordered n-tuples (extremely rare). If a
relationship exists among the entities, then all must be present. E.g.
INSTRUCTOR ,STUDENTS, rooms and a particular COURSE
18
BY: MA
19. … Relationship Sets
Cardinality
– the actual number of related occurrences for each of the two entities
– is the number of entity instances to which another entity set can
map under the relationship.
One-to-one: X-Y is 1:1 when each entity in X is associated
with at most one entity in Y, and each entity in Y is
associated with at most one entity in X. eg dept-headdept
One-to-many: X-Y is 1:M when each entity in X can be
associated with many entities in Y, but each entity in Y is
associated with at most one entity in X. eg deptemployee
Many-to-many: X:Y is M:M if each entity in X can be
associated with many entities in Y, and each entity in Y is
associated with many entities in X ("many" =>one or more
and sometimes zero)
BY: MA
20. Cont…
Existence
– denotes whether the existence of an entity instance is
dependent upon the existence of another, related, entity
instance
Mandatory: every instance of one entity must participate in a
relationship with another entity.
Optional: any instance of one entity might participate in a
relationship with another entity, but this is not compulsory.
BY: MA
22. E/R Diagram
Rectangles - for the Entity sets,
– Double border Rectangles - for the weak entity sets.
Ellipses - for the Attributes,
– Double border Ellipses - for the multi-valued attributes.
– Dashed border Ellipses - for the derived attributes.
– Composite attributes are represented by linked ellipses.
Diamonds - for the Relationships, and
Lines - for the links between the attributes and the entity sets
and between the entity sets and the relationships.
– Arrow Head Line - for the link between an entity set with many-to-
one relationship.
The arrow is headed to the one side entity set.
22
BY: MA
24. Example on Requirement Analysis
The problem is to design a database system for “X
Household and Office Furniture P.L.C” based on the
following information.
– The information are kept on daily basis about what the
employees do, what resource they use, which furniture are
made out of the resource, and all the sale and order records.
– Furniture is produced by an employee from resource (s).
– Every furniture is described by the furniture Id, catalog no,
model type, color, production start date, production complete
date and price; and every resource is described by stock no,
type, current cost, and avail quantity.
– A sale of furniture is made with a receipt for both regular
customers and buyers.
24
BY: MA
25. … Example on Requirement
Analysis
Regular customers are described by customer Id, name,
address and contact person; where as, no detail record is
established for buyers.
Orders for furniture are allowed only for regular customers and
in ordering a furniture, the customer may pay part of the total
price and left in debt, then pay the debt in some other time.
For the payment transactions three types of receipt are used;
one for sale, one for order and one for due payment (debt).
A single receipt of each type is prepared only for one buyer or
customer but a number of furniture can be sold or ordered by
one receipt.
Every receipt is prepared by Sales and it has receipt number,
prepared date, total price, and tax.
25
BY: MA
26. Draw ER diagram for the previous requirement
analysis?
1. Identify the entities
2. Obtain the attributes of the entity
3. Identify the relation ship between the entities
• Entity : • Relationship • Attributes
• Furniture
• Resources
• employees
• Sales
• customers
• receipt
• Order
• Produced
• sold
• Furniture :fid,---
• employees :eid--
• Sales :id
• customers
• receipt
BY: MA
28. Exercise1
Requirements of the university (oversimplified for
illustrative purposes)
– In a University database we might have entities for
Students, Modules and Lecturers.
– Students might have attributes such as their ID, Name, and
Course whereas Lecturers might have attributes such as
LID, Name, Rank and Modules might have attributes such
as ModuleNumber, ModuleName, CrHr and could have
relationships (studies) with Student and Modules and
(tutor) with Lecturers and Modules.
Identify entity, Attributes and relationship?
Draw the ER Diagram from the above requirement analysis?
BY: MA
29. Exercsise2: Country Bus Company
A Country bus Company owns a number of buses. Each bus is
allocated to a particular route, although some routes may have
several buses. Each route passes through a number of towns. One
or more drivers are allocated to each stage of a route, which
corresponds to a journey through some or all of the towns on a route.
Some of the towns have a garage where buses are kept and each of
the buses are identified by the registration number and can carry
different numbers of passengers, since the vehicles vary in size and
can be single or double-decked. Each route is identified by a route
number and information is available on the average number of
passengers carried per day for each route. Drivers have an
employee number, name, address, and sometimes a telephone
number.
30. Further on E/R Diagram
Relationship Attributes
– Attribute (s) may be used in some relationships to describe the
relationship further
Multi-way Relationship
– multi-way relationship can be reduced to a binary relationship with
the use of
an entity set in place of the relationship, and
having new relationships for the links in between the participating
entity sets and the relationship.
Cardinality Limits of a Relationship:
– 0..* or 0..∞
– 1..* or 1..∞
– 0..1
30
BY: MA
31. . . . Further on E/R Diagram
Entity Set Roles in a Relationship
– Label on the link line identifies the role
– Example:
If only two customers are allowed to make an order jointly as
Primary and Secondary
Participation in a Relationship
– Total
every element of the entity set is at least related to one element
in the other entity set
– Example:
The Furniture entity set in the Produced relationship.
– Partial
There at least one element that is not related to any element in
the other set
31
BY: MA
33. Design Issues
Faithfulness
– classes or entity sets and their attributes should reflect reality
Avoiding Redundancy
– be careful to say everything only once
Simplicity
– avoid introducing more elements into your design than are absolutely
necessary
Picking the Right kind of Element
– Entity Set versus Attributes
– Entity versus Relationship Sets
– Binary versus n-ary Relationship Sets
33
BY: MA
34. Remarks on Designing
Choose meaningful naming for the entities,
attributes and relationships.
Use short links.
Cluster diagram if it has too many entities and
relationships.
34
BY: MA
35. Keys
Keys are attributes or set of attributes that can be used to
uniquely identify an entity within the entity set
Super Key also known as Super Set is then a set of one or more
attributes that can identify an entity uniquely from the entity set.
– If K is a super set (super key) then a set consisting of K is
also a super set.
Candidate Key is the minimal super set. a Group of columns,
that uniquely identifies a row in a table.
– If the Candidate Key is selected as a key for an entity set then it said to
Primary Key.
– A candidate key has the properties of Uniqueness or Irreducibility
35
BY: MA
36. Relational Constraints/Integrity Rules
and keys:
Each row of a table is uniquely identified by a PRIMARY KEY
A primary key in E/R model is represented by underlining the attribute or
set of attributes.
A column or combination of columns that matches the primary key of
another table is called a FOREIGN KEY which is used to cross-reference
tables.
ENTITY INTEGRITY RULE of the model states that no component of the
primary key may contain a NULL value.
REFERENTIAL INTEGRITY RULE : for every foreign key value in a
table there must be a corresponding primary key value in another table in
the database.
Domain constraints/ INTEGRITY
– are requirements on an attribute value to be in a specified range of values.
BY: MA
37. Enhanced E/R Modeling
Week Entity Set
Specialization and Generalization
Aggregation
37
BY: MA
38. Week Entity Set
weak entity is uniquely identified with the help of
other entity
The strong entity which contributes its primary key is
called the identifying or owner/dominant entity set.
Criteria for weak entity set
– A one-to-many relationship set that relates the weak entity
set with owner entity set known as identifying relationship
or supporting relationship must exist.
– Total participation in the identifying relationship is required.
38
BY: MA
39. … Week Entity Set
An attribute or set attributes with in the weak
entity set referred to as discriminator is used
to distinguish weak entities.
Key of a weak entity set:
– Zero or more of its own attribute;
discriminator
– Key attributes of the owner (identifying)
entity set.
39
BY: MA
40. … Week Entity Set
Notations
– Weak Entity sets are represented by
Double boarder Rectangles.
– The identifying many-to-one relationship is
represented by
Double border Diamonds.
– If the entity set has a discriminator then it is
represented by
Underlining the attribute(s)
40
BY: MA
41. … Example (Weak entity sets)
– Each employee may have a number of Dependents.
For each dependent, we keep track of their name, sex, birth
date, and relationship to the employee.
41
Employee DEPENDANT
Depenedent on
Name Descr
Eid
Descr
Name
BY: MA
42. Specialization and Generalization
Specialization: Specialization is the process of defining a set of
subclasses of an entity type; this entity type is called the superclass of
the specialization. The set of subclasses that forms a specialization is
defined on the basis of some distinguishing characteristic of the entities
in the superclass.
– top-down process in grouping of entities that are similar in some way and distinct in
some other ways in which distinctions are made explicitly
– For example, the set of subclasses {SECRETARY,ENGINEER, TECHNICIAN} is a
specialization of the superclass EMPLOYEE that distinguishes among employee
entities based on the job type of each employee entity.
– The specialization of the EMPLOYEE entity type may yield the set of
subclasses {SALARIED_EMPLOYEE, HOURLY_EMPLOYEE}; this
specialization distinguishes among employees based on the method of pay
– Attributes that apply only to entities of a particular subclass—such as
TypingSpeed of SECRETARY—eng-type of engineers. These are called
42
BY: MA
43. Generalization: The reverse of the specialization process.
– Several classes with common features are generalized into a superclass; original
classes become its subclasses
– the generalization process can be viewed as being functionally the inverse of the
specialization process.
– bottom-up approach in which multiple entity sets are synthesized into
a higher level entity set based on their common features.
– Example: CAR, TRUCK generalized into VEHICLE Because they have
several common attributes, they can be generalized into the entity
type VEHICLE, ; both CAR, TRUCK become subclasses of the superclass
VEHICLE. We can view {CAR, TRUCK} as a specialization of VEHICLE
– Alternatively, we can view VEHICLE as a generalization of CAR and
TRUCK
– EMPLOYEE as a generalization of SECRETARY, TECHNICIAN, and
44. … Example (Specialization & Generalization)
44
EMPLOYEES
ISA
ULL-TIME
EMPLOYEE
S
PART-TIME
EMPLOYEE
S
BY: MA
45. Constraints on Specialization and Generalization
Condition-defined vs. User-defined Lower-level Entity Sets
– Condition defined: In some specializations we can determine exactly the
entities that will become members of each subclass by placing a
condition on the value of some attribute of the superclass. For example,
if the EMPLOYEE entity type has an attribute Job_type, as shown in
Figure 8.4, we can specify the condition of membership in the
SECRETARY subclass by the condition (Job_type = ‘Secretary’)
satisfying an explicit condition or predicate
– User-defined: the Membership in such a subclass is determined by the
database user when they apply the operation to add an entity to the
subclass.
determined upon the entry of the entities
45
BY: MA
46. Disjoint vs. Overlapping Specialization
– Disjoint: Specifies that the subclasses of the specialization must
be disjointed (an entity can be a member of at most one of the
subclasses of the specialization)
– Eg an EMPLOYEE can be HOURLY_EMPLOYEE or a
ALARIED_EMPLOYEE. Specified by ‘d’ in EER diagram
– Overlapping: If not disjointed, overlap; that is the same entity may
be a member of more than one subclass of the specialization
allows for a higher-level entity to belong to more than one
entity
Eg: employee can be manager also employee
Specified by ‘O’ in EER diagram
47. Constraints on Specialization and
Generalization
Total vs. Partial Specialization or Generalization:
– The second constraint on specialization is called the completeness (or
totalness) constraint, which may be total or partial.
– A total specialization constraint specifies that every entity in the
superclass must be a member of at least one subclass in the
specialization. Higher level entity must belong to one of the lower-level
entity, For example, if every EMPLOYEE must be either an
HOURLY_EMPLOYEE or a SALARIED_EMPLOYEE,
– a partial specialization, which allows an entity not to belong to any of
the subclasses. For example, if some
EMPLOYEE entities do not belong to any of the subclasses
{SECRETARY, ENGINEER, TECHNICIAN}
Generalization usually is total because the superclass is derived from
47
BY: MA
48. Aggregation
E/R modeling allows relationships only between
entity sets.
It achieve the relationship between a
relationship and an entity set or a collection of
entity sets.
– Aggregation is an abstraction through which
collection of related entity sets and relationships are
treated as high-level entities.
– It allows indicating for a relationship set (identified
through a box) to participate in another relationship
set.
48
BY: MA
52. 1. Map Regular/strong Entity Types
For each regular (strong) entity type E in the ER schema,
create a relation R that includes all the simple attributes of E.
Choose one of the key attributes of E as the primary key for R.
If the chosen key of E is composite, the set of simple attributes
that form it will together form the primary key of R.
BY: MA
53. 2. Map Weak Entity Types
For each weak entity type W in the ER schema with owner
entity type E, create a relation R & include all simple
attributes (or simple components of composite attributes) of
W as attributes of R.
Also, include as foreign key attributes of R the primary key
attribute(s) of the relation(s) that correspond to the owner
entity type(s).
The primary key of R is the combination of the primary
key(s) of the owner(s) and the partial key of the weak entity
type W, if any.
BY: MA
55. 3. Map Binary 1:1 Relation Types
For each binary 1:1 relationship type R in the ER schema,
identify the relations S and T that correspond to the entity
types participating in R.
Choose one of the relations-say S-and include a foreign key
in S the primary key of T. It is better to choose an entity type
with total participation in R in the role of S.
BY: MA
57. 4. Map Binary 1:N Relationship Types.
For each regular binary 1:N relationship type R, identify
the relation S that represent the participating entity type at
the N-side of the relationship type.
Include as foreign key in S the primary key of the relation
T that represents the other entity type participating in R.
Include any simple attributes of the 1:N relation type as
attributes of S.
BY: MA
59. 5. Map Binary M:N Relationship Types.
For each regular binary M:N relationship type R, create a
new relation S to represent R.
Include as foreign key attributes in S the primary keys of
the relations that represent the participating entity types;
their combination will form the primary key of S.
Also include any simple attributes of the M:N relationship
type (or simple components of composite attributes) as
attributes of S.
BY: MA
61. 6. Map Multivalued attributes.
For each multivalued attribute A, create a new relation R.
This relation R will include an attribute corresponding to A,
plus the primary key attribute K-as a foreign key in R-of
the relation that represents the entity type of relationship
type that has A as an attribute.
The primary key of R is the combination of A and K. If the
multivalued attribute is composite, we include its simple
components.
BY: MA
63. For each n-ary relationship type R, where n>2, create a
new relationship S to represent R.
Include as foreign key attributes in S the primary keys of
the relations that represent the participating entity types.
Also include any simple attributes of the n-ary
relationship type (or simple components of composite
attributes) as attributes of S.
BY: MA