Chapter 2: Modeling Data in the Organization

Name: Chapter 2: Modeling Data in the Organization
Uploaded: 2017-10-11T08:07:31+00:00
Duration: PTM35S28
Channel: Anastasia Owens
Description: Chapter 2: Modeling Data in the Organization

Chapter 2: Modeling Data in the Organization
Modern Database Management 11th Edition Jeffrey A. Hoffer, V. Ramesh, Heikki Topi

Objectives Define terms Understand importance of data modeling
Write good names and definitions for entities, relationships, and attributes Distinguish unary, binary, and ternary relationships Model different types of attributes, entities, relationships, and cardinalities Draw E-R diagrams for common business situations Convert many-to-many relationships to associative entities Model time-dependent data using time stamps 【】

E-R MODEL CONSTRUCTS (1)
Entities: Entity instance–object, person, place, event, concept (often corresponds to a row in a table) Entity Type–collection of entities (often corresponds to a table) 【Definition of entities P. 58】 (format to follow for your HW/proj) Entity type: UNIVERSITY; entity instances? is there an attribute Student_Last_Name in the above? is there an attribute Name_of_Department in the above? Entity type: DEPARTMENT; entity instances? 2

DISCUSSION Entity Attributes
Type of entities–object, person, place, event, concept Entity Attributes object Ex: Bottled water place Ex: State Ex: City people Ex: Student Ex: Patient event Ex: Stud-org-sponsored campus activities Think: City names in State table? Similarly: UNIV, COLLEGE, FACULTY, STUDENT

Attributes: Properties or characteristics of an entity or relationship type (often corresponds to a field/column in a table) 2

Relationships: Relationship instance–link between entities (entity instances) (corresponds to primary key-foreign key equivalencies in related tables) 【Relationship type】–category of relationship…link between entity types 【Descriptions 】P. 59 (REQUIRED format for your HW/proj) (often corresponds to ___/______ among tables) Try to state a relationship instance? Such as one that is between entity types STUDENT and COURSE? 2

Summary and comparison of basic terms
In Business In DB Concept In DB Implementation Remark Biz function Entity type Entity instance Attribute Relationship *(“num-ber”) 7

Sample E-R Diagram (Figure 2-1)
Explanation of entities: P.58; business rules: P.59 – important, and useful! 3

E-R Diagram Notation – Chen (1976)

E-R Diagram: Chen Notation
Boxes represent entities Ovals represent attributes Diamonds represent relationships

© 2013 Pearson Education, Inc. Publishing as Prentice Hall
Basic E-R notation (Figure 2-2) Entity symbols Attribute symbols A special entity that is also a relationship Relationship symbols Relationship degrees specify number of entity types involved (unary, binary, ternary) Relationship cardinalities specify # entity instances in the other end of the relationship each entity instance in this end is allowed to associate © 2013 Pearson Education, Inc. Publishing as Prentice Hall Chapter 2 8

Modeling the Rules of an Org
P. 60: “what data modeling is all about?” – To document rules and policies of an organization! Business rules and policies govern – Creating, {ex: enrollment record} Updating, {ex: units attempted; units earned} Removing {ex: customer credit card number} data in an info storage and processing system Business rules and policies must be described along with the data to which they are related

Business Rules Are statements that define or constrain some aspect of the business Are derived from policies, procedures, events, functions Assert business structure Control/influence business behavior Are expressed in terms familiar to end users Are automated through DBMS software Relationships in an ERD are defined/derived from business rules

Overview of Business Rules (1)
Are statements that define or constrain some aspect of the business Are derived from policies, procedures, events, functions Assert business structure Control/influence business behavior Are expressed in terms familiar to end users Are automated through DBMS software P. 60: “what data modeling is all about?”

Overview of Business Rules (2)
Are statements that define or constrain some aspect of the business Syntax of business rules: ENTITY_1 Relationiship_Verb_Phrase number ENTITY_2 Where Relationiship_Verb_Phrase = Cardinality_adverb + Relationship_Verb Examples: ENTITY_1 May/Must Do/Have number ENTITY_2 STUDENT may have many ENROLLMENT CAR must be registered to at least one OWNER CUSTOMER must be served by only one EMPLOYEE Two examples P. 61 – think about more examples of yours?

A Good Business Rule Is: (Table 2-1, P.62)
Declarative–what, not how Precise–clear, agreed-upon meaning Atomic–one statement Consistent–internally and externally Expressible–structured, natural language Distinct–non-redundant Business-oriented–understood by business people Excellent examples: P. 59

Excellent examples: P. 58 A Good Data Name Is:
Related to business, not technical, characteristics Meaningful and self-documenting Unique Readable Composed of words from an approved list Repeatable - different people would develop same name Written in standard syntax Excellent examples: P. 58

Salin’s (1990) suggestion on data name
Preparing a definition of the data Removing insignificant words Arranging the words in a meaningful, repeatable way Assigning a standard abbr for each word Use qualifiers if needed

Data Definitions Explanation of a term or fact
Term–word or phrase with specific meaning Fact–association between two or more terms Examples: P.64 Guidelines for good data definition A concise description of essential data meaning Gathered in conjunction with systems requirements Accompanied by diagrams Achieved by consensus, and iteratively refined

Modeling Entities and Attributes
The E-R model is most used as a tool for communications between database designers and end users during the analysis phase of database development

Kinds of entities: P.66 Entities Entity – a person, a place, an object, an event, or a concept in the user environment about which the organization wishes to maintain data Entity type – a collection of entities that share common properties or characteristics TRUCK // STUDENT Entity instance – A single occurrence of an entity type 2013 Chevy Tahoe // John Smith, ACCT

An Entity… SHOULD BE: We use capital for names of entity types
An entity has many instances. Ex: FACULTY has Jeff Zhang, David Liu… SHOULD BE: An object that will have many instances in the database An object that will be composed of multiple attributes An object that has relationship w other object(s) An object that we are trying to model SHOULD NOT BE: A user of the database system An output of the database system (e.g., a report) We use capital for names of entity types Implementation?

Entity Type and Entity Instances
Value of an attribute

Inappropriate entities
Figure 2-4 Example of inappropriate entities System user System output Inappropriate entities Appropriate entities

Strong vs. Weak Entities, and Identifying Relationships
Strong entity exists independently of other types of entities has its own unique identifier identifier underlined with single line Weak entity dependent on a strong entity (identifying owner)…cannot exist on its own does not have a unique identifier (only a partial identifier) entity box and partial identifier have double lines Identifying relationship links strong entities to weak entities – double line - Uses the identifier of the strong entity as its identifier

Figure 2-5 Example of a weak identity and its identifying relationship
Strong entity Weak entity

Naming and defining entity types
Singular noun Specific to the organization Abbr can be used; follow same rules Named for result of event, not the process Consistent Defining (more see P71): What entity instances are included and not included Often includes when an instance is created/ For some entity types: what history to be kept 5

Attributes Attribute–property or characteristic of an entity or relationship type Every entity instance has its own set of values for the attributes of the entity (when each attribute has a specific value, …) Classifications of attributes: Required versus Optional Attributes Simple versus (Composite Attribute) Single-Valued versus {Multivalued Attribute} Stored versus Derived Attributes Identifier Attributes 5

Required vs. Optional Attributes
Required – must have a value for every entity (or relationship) instance with which it is associated Optional – may not have a value for every entity (or relationship) instance with which it is associated 5

Simple vs. Composite Attributes
Composite attribute – An attribute that has meaningful component parts (attributes) The address is broken into component parts Figure 2-7 A composite attribute Example? 6

Multi-valued and Derived Attributes
Multivalued – may take on more than one value for a given entity (or relationship) instance Derived – values can be calculated from related attribute values (not physically stored in the database) Figure 2-8 Entity with multivalued attribute (Skill) and derived attribute (Years Employed) Multivalued an employee can have more than one skill Derived Calculated from date employed and current date Example: © 2013 Pearson Education, Inc. Publishing as Prentice Hall Chapter 2 12

Identifiers (Keys) Identifier (Key)–an attribute (or combination of attributes) that uniquely identifies individual instances of an entity type Simple versus Composite Identifier An order line item is identified with… Candidate Identifier–an attribute that could be a key…satisfies the requirements for being an identifier 6

Criteria for Identifiers
Choose Identifiers that Will not be null Unique for each instance in the entity Will not change in value Avoid intelligent identifiers (e.g., containing locations or people that might change) Substitute new, simple keys for long, composite keys 7

Naming Attributes Name should be a singular noun or noun phrase
Name should be unique Name should follow a standard format e.g. [Entity type name { [ Qualifier ] } ] Class Similar attributes of different entity types should use the same qualifiers and classes 7

Defining Attributes State what the attribute is and possibly why it is important Make it clear what is and is not included in the attribute’s value Include aliases in documentation State source of values Specify required vs. optional State min and max number of occurrences allowed Indicate relationships with other attributes 7

Intro to relationship An association representing an interaction among the instances of one or more entity types – P.75 A relationship has a verb name A name that describes the nature of the relationship - examples: STDENT takes COURSE, MANAGER supervises EMPLOYEE, ENGINEER is assigned to PROJECT, PART is used in PRODUCT… Think about one that involves an organization? 5

Modeling Relationships
Relationship Types vs. Relationship Instances The relationship type is modeled as lines between entity types the relationship instance is between specific entity instances Relationships can have attributes These describe features pertaining to the association between the entities in the relationship Two entities can have more than one type of relationship between them (multiple relationships) Associative Entity–combination of relationship and entity (“relationship-turned-entity”)

Figure 2-11a A relationship with an attribute
Here, the date completed attribute pertains specifically to the employee’s completion of a course…it is an attribute of the relationship Please note that the above relationship is a many-to-many. What if it is one-to-many? Can we do the same re “Date-completed”? “Grade”? 20

Associative Entities An entity–has attributes
A relationship–links entities together Associative Entity–combination of relationship and entity (“relationship-turned-entity”) Whether or not to convert a relationship to an associative entity type? – four conditions (P 78) Many-to-many Resulting entity type has independent meaning, and can be identified Has one or more attributes in addition to … The associative entity participates in relationship(s) independent of the entities related in the associated relationship (P.80) Ternary relationships should ALWAYS be converted to associative entities

Figure 2-11b An associative entity (CERTIFICATE)
Associative entity is like a relationship with an attribute, but it is also considered to be an entity in its own right Note that the many-to-many cardinality between entities in Figure 2-11a has been replaced by two one-to-many relationships with the associative entity (Note that min cardinalities are missing above for the associative entity) P. 79, second paragraph 21

Online references of E-R diagram
A concise but fairly complete E-R model quick reference: E-R diagram elements (Chen and crow’s foot), with examples 16

Degree of Relationships
Degree of a relationship is the number of entity types that participate in it Unary Relationship Between instances of a single entity Binary Relationship Between instances of two entities Ternary Relationship Between instances of three entities Compared w cardinality (Slide 55~): # of entity instances associated 16

Degree of relationships – from Figure 2-2 One entity related to another of the same entity type Entities of two different types related to each other Entities of three different types related to each other © 2013 Pearson Education, Inc. Publishing as Prentice Hall Chapter 2 8

Figure 2-12 Examples of relationships of different degrees
a) Unary relationships 22

Figure 2-12 Examples of relationships of different degrees (cont.)
b) Binary relationships 22

Note: a relationship can have attributes of its own
Figure 2-12 Examples of relationships of different degrees (cont.) c) Ternary relationship Note: a relationship can have attributes of its own 22

Figure 2-13c An associative entity – bill of materials structure
This could just be a relationship with attributes…it’s a judgment call 27

Figure 2-14 Ternary relationship as an associate entity
Guidelines: PP.82~83 22

More cases of ternary relationships?
STUDENT – COURSE – FACULTY? PATIENT – TREATMENT – DOCTOR? Guidelines: PP.82~83 22

Attributes or entity? Fig 2-15a

Attributes or entity? Fig 2-15b

Attributes or entity? Fig 2-15c

Figure 2-13c An associative entity – bill of materials structure This could just be a relationship with attributes…it’s a judgment call. © 2013 Pearson Education, Inc. Publishing as Prentice Hall Chapter 2 27

# entity INSTANCEs related
Cardinality of Relationships Watch out the difference between Degree of relationship And Cardinality!! # entities involved # entity INSTANCEs related

Cardinality of Relationships
Must examine from BOTH sides to determine One-to-One Each entity instance in the relationship (“A”) will have exactly one related entity (“B”) One-to-Many An entity instance (in “A”) on one side of the relationship can have many related entity instances (in “B”), but an entity instance on the other side will have a maximum of one related entity instance Many-to-Many Entity instances on both sides of the relationship can have many related ent. Inst. on the other side

Cardinality Constraints
Cardinality Constraints—the number of instances of one entity (“B”) that can or must be associated with each instance of another entity (“A”) When you view a relationship from one entity to another: the number of instances of “ending” entity that can or must be associated with each instance of “starting” entity Minimum Cardinality If zero, then optional If one or more, then mandatory Maximum Cardinality - The max number 29

Fig 2-16 Introducing Cardinality Constraints
Use the “starting” & “ending” to think about cardinalities

Basic E-R notation (Figure 2-2; portion)
Relationship cardinalities specify - for EACH instance on the “starting entity type,” the # of instances on the “ending entity type” is allowed {“starting” and “ending” here refer to direction of rela.} Maximum one Maximum many Minimum one Minimum zero 60 8

ONE-TO-ONE (From my own IS 312 PPT)
One-to-one (1:1) – A relationship between two entities in which an instance of entity A can be related to only one instance of entity B; and an entity B instance can be related to only one instance of entity A Chen Has (1) Located-in (1) Info Engi TOWN Has AIRPORT

One-to-one (think about E-R Diagr)
Optional Mandatory

ONE-TO-MANY Class 3 (Week 4) resumes from here One-to-many (1:M) – A relationship between two entities, in which an instance of entity A (any instance of A) can be related to zero, one, or more instances of entity B; and an instance of entity B can be related to only one instance of entity A Has (many) Is-place-by (1) This is Chen model; Information engineering method for the same scenario see left portion of next slide

ITEM ENROLLMENT CUSTOMER DEPT COURSE ORDER Info Engring (Crow’s foot)
How many customers are there? Info Engring (Crow’s foot) Each CUSTOMER can place many ORDERs; Each ORDER is placed by Only one CUSTOMER CUSTOMER DEPT 1 1 M M COURSE ORDER 1 1 M M Try stating this relationship? ITEM ENROLLMENT

One-to-many (think about E-R Diagr)
Optional Mandatory

MANY-TO-MANY Many-to-many (M:N) – A relationship between two entities in which an instance (any instance) of entity A can be related to zero, one, or more instances of entity B; AND an instance of entity B can be related to zero, one, or more instances of entity A Orders (many) Chen Is-ordered-by (many)

many-to-many (think about E-R Diagr)
Optional Mandatory

Figure 2-17 Examples of cardinality constraints
a) Mandatory cardinalities Related slide added A patient history is recorded for one and only one patient (viewed R to L) A patient must have recorded at least one history, and can have many (viewed L to R) 1

Figure 2-17 Examples of cardinality constraints (cont.)
b) One optional, one mandatory Related slide added Use the “starting” & “ending” to think about cardinalities A project must be assigned to at least one employee, and may be assigned to many (viewed R to L) An employee can be assigned to any number of projects, or may not be assigned to any at all (viewed L to R) 1

Figure 2-17 Examples of cardinality constraints (cont.)
c) Optional cardinalities Use the “starting” & “ending” to think about cardinalities A person is married to at most one other person, or may not be married at all 1

Figure 2-18 Cardinality constraints in a ternary relationship
36

Cardinality Summary (Logic) [Observe!]
Each A each B Can/may related to ___ B, one A: Option./mand. ____ to ____ Must related to many A: must related to

Figure 2-19 Simple example of time-stamping
The Price History attribute is both multivalued and composite. Time stamp – a time value that is associated with a data value, often indicating when some event occurred that affected the data value 37

Example of time, Fig 2-20a

Example of time, Fig 2-20b

Figure 2-20c E-R diagram with associative entity for product assignment to product line over time
The Assignment associative entity shows the date range of a product’s assignment to a particular product line. Modeling time-dependent data has become more important due to regulations such as HIPAA and Sarbanes-Oxley. 37

Figure 2-21 Examples of multiple relationships
a) Employees and departments Related slide added Entities can be related to one another in more than one way 40

Figure 2-21 Examples of multiple relationships (cont.)
b) Professors and courses (fixed lower limit constraint) Here, min cardinality constraint is 2. At least two professors must be qualified to teach each course. Each professor must be qualified to teach at least one course. 40

Figure 2-22 Data model for Pine Valley Furniture Company in Microsoft Visio notation Different modeling software tools may have different notation for the same constructs.

Reiterate Cardinality (using PPT #69 as example)
Each Patient [1, LEFT entity] has recorded [2, relationship verb] at least one, up to many [3, cardinality], patient history (records) [4, RIGHT entity] Each Patient History (record) [a, RIGHT entity] has been recorded [b, relationship verb (I wrote it; not displayed)] For at least one, up to 1 (ONE) [c, cardinality], patient (records) [d, LEFT entity] 2 3 4 1 b d c a 40

M-M to Associative Entity (PPT #70 as example)
In the eyes of EMPOLYEE, PROJECT is optional many; In the eyes of PROJECT, EMPLOYEE is mandatory many. After the associative entity is introduced: The “far ends” are ALWAYS _______________________ In the eyes of EMPLOYEE, ASSIGNMENT is _________ In the eyes of PROJECT, ASSIGNMENT is ____________ EMPLOYEE ASSIGNMENT PROJECT 40

Recap of MIN/MAX (last week)
The “far ends” are Max? Min? The “near-center ends” are Min? Max? So one must always ensure that the “far ends” are never _________ 40

Figure 2-21 Examples of multiple relationships
Extension of Figure 2-21 Examples of multiple relationships c) CUSTOMER and COMPANY, in the Web 2.0 age does_business_with CUSTOMER COMPANY ________?________ Relationship 1: CUSTOMER does_business_with COMPANY Relationship 2: CUSTOMER ________________ COMPANY 40

Chapter 2: Modeling Data in the Organization

Similar presentations

Presentation on theme: "Chapter 2: Modeling Data in the Organization"— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

Chapter 2: Modeling Data in the Organization

Similar presentations

Presentation on theme: "Chapter 2: Modeling Data in the Organization"— Presentation transcript:

Similar presentations

About project

Feedback