Lecture 3 - ERD PDF

Faculty Of Computer Science Mohamed Ghoneimy , Ph.D. [email protected]  Fundamentals Of Database Systems CS 215 Lecturer 3: Data Modeling Using the Entity-Relationship (E R) Model Fundamentals of Database Systems Seventh Edition...

Faculty Of Computer Science Mohamed Ghoneimy , Ph.D. [email protected]  Fundamentals Of Database Systems CS 215 Lecturer 3: Data Modeling Using the Entity-Relationship (E R) Model Fundamentals of Database Systems Seventh Edition Chapter 3 Data Modeling Using the Entity-Relationship (ER) Model Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Overview of Database Design Process (1 of 2) Two main activities: – Database design – Applications design Focus in this chapter on conceptual database design – To design the conceptual schema for a database application Applications design focuses on the programs and interfaces that access the database – Generally considered part of software engineering Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Overview of Database Design Process (2 of 2) Figure 3.1 A simplified diagram to illustrate the main phases of database design. Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Methodologies for Conceptual Design Entity Relationship (ER) Diagrams (Chapter 3) Enhanced Entity Relationship (EER) Diagrams (Chapter 4) Use of Design Tools in industry for designing and documenting large scale designs ERD PLUS Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Example COMPANY Database (1 of 2) We need to create a database schema design based on the following (simplified) requirements of the COMPANY Database: – The company is organized into DEPARTMENTs. Each department has a name, number and an employee who manages the department. We keep track of the start date of the department manager. A department may have several locations. – Each department controls a number of PROJECTs. Each project has a unique name, unique number and is located at a single location. Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Example COMPANY Database (2 of 2) – The database will store each EMPLOYEE’s social security number, address, salary, sex, and birthdate. ▪ Each employee works for one department but may work on several projects. ▪ The DB will keep track of the number of hours per week that an employee currently works on each project. ▪ It is required to keep track of the direct supervisor of each employee. – Each employee may have a number of DEPENDENTs. ▪ For each dependent, the DB keeps a record of name, sex, birthdate, and relationship to the employee. Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved ER Model Concepts (1 of 2) Entities and Attributes – Entity is a basic concept for the ER model. Entities are specific things or objects in the mini-world that are represented in the database. ▪ For example the EMPLOYEE John Smith, the Research DEPARTMENT, the ProductX PROJECT – Attributes are properties used to describe an entity. ▪ For example an EMPLOYEE entity may have the attributes Name, SSN, Address, Sex, BirthDate Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved ER Model Concepts (2 of 2) – A specific entity will have a value for each of its attributes. ▪ For example a specific employee entity may have Name=‘John Smith’, SSN=‘123456789’, Address =‘731, Fondren, Houston, TX’, Sex=‘M’, BirthDate=‘09-JAN-55’ – Each attribute has a value set (or data type) associated with it – e.g. integer, string, date, enumerated type, … Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Types of Attributes (1 of 3) Simple – Each entity has a single atomic value for the attribute. For example, SSN or Sex. Composite – The attribute may be composed of several components. For example: ▪ Address(Apt#, House#, Street, City, State, ZipCode, Country), or ▪ Name(FirstName, MiddleName, LastName). ▪ Composition may form a hierarchy where some components are themselves composite. Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Types of Attributes (2 of 3) Multi-valued – An entity may have multiple values for that attribute. For example, Color of a CAR or PreviousDegrees of a STUDENT. ▪ Denoted as {Color} or {PreviousDegrees}. In general, composite and multi-valued attributes may be nested arbitrarily to any number of levels, although this is rare. – For example, PreviousDegrees of a STUDENT is a composite multi-valued attribute denoted by Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Types of Attributes (3 of 3) – Multiple PreviousDegrees values can exist – Each has four subcomponent attributes: ▪ College, Year, Degree, Field Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Example of a Composite Attribute Figure 3.4 A hierarchy of composite attributes. Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Entity Types and Key Attributes (1 of 2) Entities with the same basic attributes are grouped or typed into an entity type. – For example, the entity type EMPLOYEE and PROJECT. An attribute of an entity type for which each entity must have a unique value is called a key attribute of the entity type. – For example, SSN of EMPLOYEE. Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Entity Types and Key Attributes (2 of 2) A key attribute may be composite. – VehicleTagNumber is a key of the CAR entity type with components (Number, State). An entity type may have more than one key. – The CAR entity type may have two keys: ▪ VehicleIdentificationNumber (popularly called VIN) ▪ VehicleTagNumber (Number, State), aka license plate number. Each key is underlined (Note: this is different from the relational schema where only one “primary key is underlined). Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Entity Set Each entity type will have a collection of entities stored in the database – Called the entity set or sometimes entity collection Previous slide shows three CAR entity instances in the entity set for CAR Same name (CAR) used to refer to both the entity type and the entity set However, entity type and entity set may be given different names Entity set is the current state of the entities of that type that are stored in the database Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Value Sets (Domains) of Attributes Each simple attribute is associated with a value set – E.g., Lastname has a value which is a character string of upto 15 characters, say – Date has a value consisting of MM-DD-YYYY where each letter is an integer A value set specifies the set of values associated with an attribute Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Attributes and Value Sets Value sets are similar to data types in most programming languages – e.g., integer, character (n), real, bit Mathematically, an attribute A for an entity type E whose value set is V is defined as a function A :E → P(V) Where P ( V ) indicates a power set (which means all possible subsets) of V. The above definition covers simple and multivalued attributes. We refer to the value of attribute A for entity e as A(e). Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Displaying An Entity Type In ER diagrams, an entity type is displayed in a rectangular box Attributes are displayed in ovals – Each attribute is connected to its entity type – Components of a composite attribute are connected to the oval representing the composite attribute – Each key attribute is underlined – Multivalued attributes displayed in double ovals See the full ER notation in advance on the next slide Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Notation for ER Diagrams Figure 3.14 Summary of the notation for ER diagrams. Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Entity Type CAR with Two Keys and a Corresponding Entity Set Figure 3.7 The CAR entity type with two key attributes, Registration and Vehicle_id. (a) ER diagram notation. (b) Entity set with three entities. Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Initial Conceptual Design of Entity Types for the COMPANY Database Schema Based on the requirements, we can identify four initial entity types in the COMPANY database: – DEPARTMENT – PROJECT – EMPLOYEE – DEPENDENT Their initial conceptual design is shown on the following slide The initial attributes shown are derived from the requirements description Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Initial Design of Entity Types: EMPLOYEE, DEPARTMENT, PROJECT, DEPENDENT Figure 3.8 Preliminary design of entity types for the COMPANY database. Some of the shown attributes will be refined into relationships. Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Refining the Initial Design by Introducing Relationships The initial design is typically not complete Some aspects in the requirements will be represented as relationships ER model has three main concepts: – Entities (and their entity types and entity sets) – Attributes (simple, composite, multivalued) – Relationships (and their relationship types and relationship sets) We introduce relationship concepts next Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Relationships and Relationship Types A relationship relates two or more distinct entities with a specific meaning. – For example, EMPLOYEE John Smith works on the ProductX Project, or EMPLOYEE Franklin Wong manages the Research DEPARTMENT. Relationships of the same type are grouped or typed into a relationship type. – For example, the WORKS_ON relationship type in which EMPLOYEEs and PROJECTs participate, or the MANAGES relationship type in which EMPLOYEEs and DEPARTMENTs participate. The degree of a relationship type is the number of participating entity types. – Both MANAGERS and WORKS_ON are binary relationships. Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Relationship Instances of the WORKS_FOR N:1 relationship between EMPLOYEE and DEPARTMENT Figure 3.9 Some instances in the WORKS_FOR relationship set, which represents a relationship type WORKS_FOR between EMPLOYEE and DEPARTMENT Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Relationship Instances of the M:N WORKS_ON Relationship between EMPLOYEE and PROJECT Figure 3.13 An M:N relationship, WORKS_ON. Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Relationship Type V s Relationship Set (1 of 2) ersu Relationship Type: – Is the schema description of a relationship – Identifies the relationship name and the participating entity types – Also identifies certain relationship constraints Relationship Set: – The current set of relationship instances represented in the database – The current state of a relationship type Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Relationship Type V s Relationship Set (2 of 2) ersu Previous figures displayed the relationship sets Each instance in the set relates individual participating entities – one from each participating entity type In ER diagrams, we represent the relationship type as follows: – Diamond-shaped box is used to display a relationship type – Connected to the participating entity types via straight lines – Note that the relationship type is not shown with an arrow. The name should be typically be readable from left to right and top to bottom. Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Refining the Company Database Schema by Introducing Relationships By examining the requirements, six relationship types are identified All are binary relationships( degree 2) Listed below with their participating entity types: – WORKS_FOR (between EMPLOYEE, DEPARTMENT) – MANAGES (also between EMPLOYEE, DEPARTMENT) – CONTROLS (between DEPARTMENT, PROJECT) – WORKS_ON (between EMPLOYEE, PROJECT) – SUPERVISION (between EMPLOYEE (as subordinate), EMPLOYEE (as supervisor)) – DEPENDENTS_OF (between EMPLOYEE, DEPENDENT) Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved ER Diagram – Relationship Types Are: WORKS_FOR, MANAGES, WORKS_ON, CONTROLS, SUPERVISION, DEPENDENTS_OF Figure 3.2 An ER schema diagram for the COMPANY database. The diagrammatic notation is introduced gradually throughout this chapter. Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Discussion on Relationship Types In the refined design, some attributes from the initial entity types are refined into relationships: – Manager of DEPARTMENT → MANAGES – Works_on of EMPLOYEE → WORKS_ON – Department of EMPLOYEE → WORKS_FOR – etc In general, more than one relationship type can exist between the same participating entity types – MANAGES and WORKS_FOR are distinct relationship types between EMPLOYEE and DEPARTMENT – Different meanings and different relationship instances. Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Constraints on Relationships Constraints on Relationship Types – (Also known as ratio constraints) – Cardinality Ratio (specifies maximum participation) ▪ One-to-one (1:1) ▪ One-to-many (1:N) or Many-to-one (N:1) ▪ Many-to-many (M:N) – Existence Dependency Constraint (specifies minimum participation) (also called participation constraint) ▪ zero (optional participation, not existence-dependent) ▪ one or more (mandatory participation, existence- dependent) Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Many-To-One (N:1) Relationship Figure 3.9 Some instances in the WORKS_FOR relationship set, which represents a relationship type WORKS_FOR between EMPLOYEE and DEPARTMENT. Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Many-To-Many (M:N) Relationship Figure 3.13 An M:N relationship, WORKS_ON. Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Recursive Relationship Type A relationship type between the same participating entity type in distinct roles Also called a self-referencing relationship type. Example: the SUPERVISION relationship EMPLOYEE participates twice in two distinct roles: – supervisor (or boss) role – supervisee (or subordinate) role Each relationship instance relates two distinct EMPLOYEE entities: – One employee in supervisor role – One employee in supervisee role Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Displaying a Recursive Relationship In a recursive relationship type. – Both participations are same entity type in different roles. – For example, SUPERVISION relationships between EMPLOYEE (in role of supervisor or boss) and (another) EMPLOYEE (in role of subordinate or worker). In following figure, first role participation labeled with 1 and second role participation labeled with 2. In ER diagram, need to display role names to distinguish participations. Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved A Recursive Relationship Supervision` Figure 3.11 A recursive relationship SUPERVISION between EMPLOYEE in the supervisor role (1) and EMPLOYEE in the subordinate role (2). Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Recursive Relationship Type is: Supervision (Participation Role Names Are Shown) Figure 3.2 An ER schema diagram for the COMPANY database. The diagrammatic notation is introduced gradually throughout this chapter and is summarized in Figure 3.14. (see slide 51) Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Weak Entity Types (1 of 2) An entity that does not have a key attribute and that is identification-dependent on another entity type. A weak entity must participate in an identifying relationship type with an owner or identifying entity type Entities are identified by the combination of: – A partial key of the weak entity type – The particular entity they are related to in the identifying relationship type Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Weak Entity Types (2 of 2) Example: – A DEPENDENT entity is identified by the dependent’s first name, and the specific EMPLOYEE with whom the DEPENDENT is related – Name of DEPENDENT is the partial key – DEPENDENT is a weak entity type – EMPLOYEE is its identifying entity type via the identifying relationship type DEPENDENT_OF Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Attributes of Relationship Types A relationship type can have attributes: – For example, HoursPerWeek of WORKS_ON – Its value for each relationship instance describes the number of hours per week that an EMPLOYEE works on a PROJECT. ▪ A value of HoursPerWeek depends on a particular (employee, project) combination – Most relationship attributes are used with M:N relationships ▪ In 1:N relationships, they can be transferred to the entity type on the N-side of the relationship Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Example Attribute of a Relationship Type: Hours of WORKS_ON Figure 3.2 An ER schema diagram for the COMPANY database. The diagrammatic notation is introduced gradually throughout this chapter and is summarized in Figure 3.14. (see slide 51) Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Notation for Constraints on Relationships Cardinality ratio (of a binary relationship): 1:1, 1:N, N:1, or M:N – Shown by placing appropriate numbers on the relationship edges. Participation constraint (on each participating entity type): total (called existence dependency) or partial. – Total shown by double line, partial by single line. Note: These are easy to specify for Binary Relationship Types. Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Alternative (Min, Max) Notation for Relationship Structural Constraints: (1 of 2) Specified on each participation of an entity type E in a relationship type R Specifies that each entity e in E participates in at least min and at most max relationship instances in R Default(no constraint): min=0, max=n (signifying no limit) Must have min ≤ max, min ≥ 0, max ≥ 1 Derived from the knowledge of mini-world constraints Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Alternative (Min, Max) Notation for Relationship Structural Constraints: (2 of 2) Examples: – A department has exactly one manager and an employee can manage at most one department. ▪ Specify (0,1) for participation of EMPLOYEE in MANAGES ▪ Specify (1,1) for participation of DEPARTMENT in MANAGES – An employee can work for exactly one department but a department can have any number of employees. ▪ Specify (1,1) for participation of EMPLOYEE in WORKS_FOR ▪ Specify (0,n) for participation of DEPARTMENT in WORKS_FOR Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved The (Min,Max) Notation for Relationship Constraints Read the min, max numbers next to the entity type and looking away from the entity type Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Company ER Schema Diagram Using (Min, Max) Notation Figure 3.15 ER diagrams for the company schema, with structural constraints specified using (min, max) notation and role names. Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Summary of Notation for ER Diagrams Figure 3.14 Summary of the notation for ER diagrams. Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Example 1 A small company called "Fitness Plus" offers fitness classes to its members. Each member can attend zero or multiple classes, and each class can have multiple members but at least one member. Each class has a unique ID, a name, a description, and a maximum number of attendees. Each member also has a unique ID, a name, one or more email addresses, and a membership start date. The member's name is composed of the first and last name. Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Example 1 Cont. A small company called "Fitness Plus" offers fitness classes to its members. Each member can attend zero or multiple classes, and each class can have multiple members but at least one member. Each class has a unique ID, a name, a description, and a maximum number of attendees. Each member also has a unique ID, a name, one or more email addresses, and a membership start date. The member's name is composed of the first and last name. Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Example 1 Cont. Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Example 2 UPS prides itself on having up-to-date information on the processing and current location of each shipped item. To do this, UPS relies on a company- wide information system. Shipped items are the heart of the UPS product tracking information system. Shipped items can be characterized by item number (unique), weight, dimensions, insurance amount, destination, and final delivery date. Shipped items are received into the UPS system at a single retail center. Retail centers are characterized by their type, uniqueID, and address. Shipped items make their way to their destination via one or more standard UPS transportation events (i.e., flights, truck deliveries). These transportation events are characterized by a unique scheduleNumber, a type (e.g, flight, truck), and a deliveryRoute. Please create an Entity Relationship diagram that captures this information about the UPS system. Be certain to indicate identifiers and cardinality constraints. Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Example 2 Cont. Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Example 3 Consider a MOVIE database in which data is recorded about the movie industry. The data requirements are summarized as follows: Each movie is identified by title and year of release. Each movie has a length in minutes. Each has a production company, and each is classified under one or more genres (such as horror, action, drama, and so forth). Each movie has one or more directors and one or more actors appear in it. Each movie also has a plot outline. Finally, each movie has zero or more quotable quotes, each of which is spoken by a particular actor appearing in the movie. Actors are identified by name and date of birth and appear in one or more movies. Each actor has a role in the movie. Directors are also identified by name and date of birth and direct one or more movies. It is possible for a director to act in a movie (including one that he or she may also direct). Production companies are identified by name and each has an address. A production company produces one or more movies. Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved Example 3 Cont. Copyright © 2016, 2011, 2007 Pearson Education, Inc. All Rights Reserved