The Entity-Relationship Model, P. I R. Nakatsu. Data Modeling A data model is the relatively simple...
-
Upload
randall-chase -
Category
Documents
-
view
216 -
download
1
description
Transcript of The Entity-Relationship Model, P. I R. Nakatsu. Data Modeling A data model is the relatively simple...
![Page 1: The Entity-Relationship Model, P. I R. Nakatsu. Data Modeling A data model is the relatively simple representation, usually graphic, of the structure.](https://reader036.fdocuments.net/reader036/viewer/2022081605/5a4d1ad77f8b9ab059973677/html5/thumbnails/1.jpg)
The Entity-Relationship Model,
P. IR. Nakatsu
![Page 2: The Entity-Relationship Model, P. I R. Nakatsu. Data Modeling A data model is the relatively simple representation, usually graphic, of the structure.](https://reader036.fdocuments.net/reader036/viewer/2022081605/5a4d1ad77f8b9ab059973677/html5/thumbnails/2.jpg)
Data Modeling• A data model is the relatively
simple representation, usually graphic, of the structure of the database.
• The database designer usually employs data models as communication tools to facilitate interaction among the designer, the applications programmer, and the end user.
![Page 3: The Entity-Relationship Model, P. I R. Nakatsu. Data Modeling A data model is the relatively simple representation, usually graphic, of the structure.](https://reader036.fdocuments.net/reader036/viewer/2022081605/5a4d1ad77f8b9ab059973677/html5/thumbnails/3.jpg)
Entity-Relationship (ER)Modeling
The ER model serves as the basic database blueprint.
• Entity: anything about which data are to be collected and stored (corresponds to a table; represented by a rectangle)
• Attribute: a characteristic of an entity (corresponds to a column in a table)
• Relationship: describes an association between entities (represented by a line joining the two entities together).
![Page 4: The Entity-Relationship Model, P. I R. Nakatsu. Data Modeling A data model is the relatively simple representation, usually graphic, of the structure.](https://reader036.fdocuments.net/reader036/viewer/2022081605/5a4d1ad77f8b9ab059973677/html5/thumbnails/4.jpg)
Database Systems, 9th Edition
![Page 5: The Entity-Relationship Model, P. I R. Nakatsu. Data Modeling A data model is the relatively simple representation, usually graphic, of the structure.](https://reader036.fdocuments.net/reader036/viewer/2022081605/5a4d1ad77f8b9ab059973677/html5/thumbnails/5.jpg)
EntitiesSomething that users want to track.
© 2000 Prentice Hall
![Page 6: The Entity-Relationship Model, P. I R. Nakatsu. Data Modeling A data model is the relatively simple representation, usually graphic, of the structure.](https://reader036.fdocuments.net/reader036/viewer/2022081605/5a4d1ad77f8b9ab059973677/html5/thumbnails/6.jpg)
Attributes (properties)Describe the entity’s characteristics.
Entity:EmployeeAttributes:LastName, FirstName, DateOfHire, DateofBirth
![Page 7: The Entity-Relationship Model, P. I R. Nakatsu. Data Modeling A data model is the relatively simple representation, usually graphic, of the structure.](https://reader036.fdocuments.net/reader036/viewer/2022081605/5a4d1ad77f8b9ab059973677/html5/thumbnails/7.jpg)
Figure 4.3 – Depicting Attributes on an ERM
7
![Page 8: The Entity-Relationship Model, P. I R. Nakatsu. Data Modeling A data model is the relatively simple representation, usually graphic, of the structure.](https://reader036.fdocuments.net/reader036/viewer/2022081605/5a4d1ad77f8b9ab059973677/html5/thumbnails/8.jpg)
Types of Attributes
• Required vs. Optional• Simple vs. Composite• Single-valued vs. Multi-valued • Derived (or Calculated)• Identifier
Provide examples of each type.
![Page 9: The Entity-Relationship Model, P. I R. Nakatsu. Data Modeling A data model is the relatively simple representation, usually graphic, of the structure.](https://reader036.fdocuments.net/reader036/viewer/2022081605/5a4d1ad77f8b9ab059973677/html5/thumbnails/9.jpg)
Advantages and Disadvantages of Storing Derived Attributes
9
![Page 10: The Entity-Relationship Model, P. I R. Nakatsu. Data Modeling A data model is the relatively simple representation, usually graphic, of the structure.](https://reader036.fdocuments.net/reader036/viewer/2022081605/5a4d1ad77f8b9ab059973677/html5/thumbnails/10.jpg)
Identifier An attribute or attributes that name or
identify entity instances.Note: Can either be unique or
nonunique
Entity: EmployeeIdentifier 1: SocialSecurityNumberIdentifier 2: LastName, FirstName
![Page 11: The Entity-Relationship Model, P. I R. Nakatsu. Data Modeling A data model is the relatively simple representation, usually graphic, of the structure.](https://reader036.fdocuments.net/reader036/viewer/2022081605/5a4d1ad77f8b9ab059973677/html5/thumbnails/11.jpg)
Relationship Types• One-to-Onee.g., one dean to one university
one head-of-state to one country• One-to-Manye.g., one painter paints many paintings
one customer places many orders• Many-to-Manye.g., students enroll in courses
![Page 12: The Entity-Relationship Model, P. I R. Nakatsu. Data Modeling A data model is the relatively simple representation, usually graphic, of the structure.](https://reader036.fdocuments.net/reader036/viewer/2022081605/5a4d1ad77f8b9ab059973677/html5/thumbnails/12.jpg)
Determining the Relationship type: 1:1,
1:M, M:NTwo questions to identify the
relationship type between A and B:– How many instances of B are related
to one instance of A?– How many instances of A are related
to one instance of B?
![Page 13: The Entity-Relationship Model, P. I R. Nakatsu. Data Modeling A data model is the relatively simple representation, usually graphic, of the structure.](https://reader036.fdocuments.net/reader036/viewer/2022081605/5a4d1ad77f8b9ab059973677/html5/thumbnails/13.jpg)
Cardinality in an ER Diagram
Cardinality expresses the minimum and maximum (min, max) number of entity occurrences associated with one occurrence of the related entity.
![Page 14: The Entity-Relationship Model, P. I R. Nakatsu. Data Modeling A data model is the relatively simple representation, usually graphic, of the structure.](https://reader036.fdocuments.net/reader036/viewer/2022081605/5a4d1ad77f8b9ab059973677/html5/thumbnails/14.jpg)
Expressing Minimum Cardinality:
Hash Marks and OvalsHash mark (or vertical line): indicates a
mandatory relationship (min cardinality of 1)
Circle: indicates an optional relationship (min cardinality of 0)
![Page 15: The Entity-Relationship Model, P. I R. Nakatsu. Data Modeling A data model is the relatively simple representation, usually graphic, of the structure.](https://reader036.fdocuments.net/reader036/viewer/2022081605/5a4d1ad77f8b9ab059973677/html5/thumbnails/15.jpg)
Expressing Optional/Mandatory Relationships
On ER Diagram
![Page 16: The Entity-Relationship Model, P. I R. Nakatsu. Data Modeling A data model is the relatively simple representation, usually graphic, of the structure.](https://reader036.fdocuments.net/reader036/viewer/2022081605/5a4d1ad77f8b9ab059973677/html5/thumbnails/16.jpg)
ER Diagram Problem 1• Acme Insurance Company employs hundreds of
claims adjustors across the U.S. As part of its agreement when joining the company, each adjustor is assigned to a company automobile.
• A claims adjustor works on a number of insurance claims. Sometimes a team of adjustors (two or more adjustors) will work together on a single claim, and there is always at least one adjustor assigned to a claim.
Draw the ER Diagram for this situation. Include
relationship types using crow’s foot notation, cardinalities in parentheses notation, and hash marks / circles to indicate optional/mandatory relationships.
![Page 17: The Entity-Relationship Model, P. I R. Nakatsu. Data Modeling A data model is the relatively simple representation, usually graphic, of the structure.](https://reader036.fdocuments.net/reader036/viewer/2022081605/5a4d1ad77f8b9ab059973677/html5/thumbnails/17.jpg)
Existence Dependence
17
Existent Dependent Existent Independent
Entity exists in the database only when it is associated with another related entity occurrence.
Entity exists apart from all of its related entities
Referred to as a strong entity or regular entity.
![Page 18: The Entity-Relationship Model, P. I R. Nakatsu. Data Modeling A data model is the relatively simple representation, usually graphic, of the structure.](https://reader036.fdocuments.net/reader036/viewer/2022081605/5a4d1ad77f8b9ab059973677/html5/thumbnails/18.jpg)
Weak Entity• Conditions
– Existence-dependent – Has a primary key that is partially or
totally derived from parent entity in the relationship
– An entity that is not weak is called a strong entity.
18
![Page 19: The Entity-Relationship Model, P. I R. Nakatsu. Data Modeling A data model is the relatively simple representation, usually graphic, of the structure.](https://reader036.fdocuments.net/reader036/viewer/2022081605/5a4d1ad77f8b9ab059973677/html5/thumbnails/19.jpg)
Weak Entity Examples
Example 1:Building (BuildingName)Apartment (BuildingName, Apartment#)
Example 2:Employee (EmployeeNo)Dependent (EmployeeNo, DependentNo)
![Page 20: The Entity-Relationship Model, P. I R. Nakatsu. Data Modeling A data model is the relatively simple representation, usually graphic, of the structure.](https://reader036.fdocuments.net/reader036/viewer/2022081605/5a4d1ad77f8b9ab059973677/html5/thumbnails/20.jpg)
Two Types of Relationships
HAS-A relationships: The term is used because an entity has a relationship with another entity (1:1, 1:M, M:N)
IS-A relationships: This term refers to relationships between super-types and sub-types.
![Page 21: The Entity-Relationship Model, P. I R. Nakatsu. Data Modeling A data model is the relatively simple representation, usually graphic, of the structure.](https://reader036.fdocuments.net/reader036/viewer/2022081605/5a4d1ad77f8b9ab059973677/html5/thumbnails/21.jpg)
Entity Supertypes and Subtypes
• Entity supertype – Generic entity type related to one or
more entity subtypes– Contains common characteristics
• Entity subtype– Contains unique characteristics of
each entity subtype
![Page 22: The Entity-Relationship Model, P. I R. Nakatsu. Data Modeling A data model is the relatively simple representation, usually graphic, of the structure.](https://reader036.fdocuments.net/reader036/viewer/2022081605/5a4d1ad77f8b9ab059973677/html5/thumbnails/22.jpg)
Database Systems, 9th Edition 22
![Page 23: The Entity-Relationship Model, P. I R. Nakatsu. Data Modeling A data model is the relatively simple representation, usually graphic, of the structure.](https://reader036.fdocuments.net/reader036/viewer/2022081605/5a4d1ad77f8b9ab059973677/html5/thumbnails/23.jpg)
Database Systems, 9th Edition 23
![Page 24: The Entity-Relationship Model, P. I R. Nakatsu. Data Modeling A data model is the relatively simple representation, usually graphic, of the structure.](https://reader036.fdocuments.net/reader036/viewer/2022081605/5a4d1ad77f8b9ab059973677/html5/thumbnails/24.jpg)
Disjoint and Overlapping Subtypes
• Disjoint subtypes (denoted by d)– Each entity instance of the supertype
can appear in only one of the subtypes.• Overlapping subtypes (denoted
by o)– Each entity instance of the supertype
can appear in more than one subtype.
![Page 25: The Entity-Relationship Model, P. I R. Nakatsu. Data Modeling A data model is the relatively simple representation, usually graphic, of the structure.](https://reader036.fdocuments.net/reader036/viewer/2022081605/5a4d1ad77f8b9ab059973677/html5/thumbnails/25.jpg)
Completeness ConstraintSpecifies whether a supertype occurrence
must be a member of at least one subtype• Partial completeness
– Symbolized by a circle over a single line– Some supertype occurrences are not members
of any subtype• Total completeness
– Symbolized by a circle over a double line– Every supertype occurrence must be a member
of at least one subtype
![Page 26: The Entity-Relationship Model, P. I R. Nakatsu. Data Modeling A data model is the relatively simple representation, usually graphic, of the structure.](https://reader036.fdocuments.net/reader036/viewer/2022081605/5a4d1ad77f8b9ab059973677/html5/thumbnails/26.jpg)
Database Systems, 9th Edition 26
![Page 27: The Entity-Relationship Model, P. I R. Nakatsu. Data Modeling A data model is the relatively simple representation, usually graphic, of the structure.](https://reader036.fdocuments.net/reader036/viewer/2022081605/5a4d1ad77f8b9ab059973677/html5/thumbnails/27.jpg)
ER Diagram Problem 2• ABC University is made up of several
departments. Each department employs several professors, and each professor is always assigned to a single department. A rule in the university stipulates that a department must consist of between 4 and 20 professors, inclusive.
• Each department is chaired by a department chair, who is a professor.
Draw the ER Diagram for this situation.