Handout 2. A very brief intro to relational databases (with more coming later). Conceptual Data Modeling Entity-Relationship Diagrams.

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Percival Wilson
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1 Handout 2 CS-605 Data Management and Systems Modeling Spring 18 Page 1 of 8 Handout 2 A very brief intro to relational databases (with more coming later). Conceptual Data Modeling Entity-Relationship Diagrams. Evolution of DB Systems Flat files s s Hierarchical 1970s s Network 1970s s Relational 1980s - present Object-oriented 1990s - present Object-relational 1990s - present Data warehousing 1980s - present Web-enabled 1990s present Cloud databases 2000 present NoSQL databases present Relational Databases Organize Data in Tables Each column is a Field (a.k.a attribute) Each row is a Record (a.k.a instance, tuple) May seem simple, but Example: poorly designed database. The purpose of this table is to keep track of students, their majors, faculty advisors, their addresses and office numbers. St_ID St_FName St_LName Major AdvFName AdvLName Adv Office 001 Adam Fisk Literature William Shakespeare ws@lu.ac.uk Sandra Smith Literature James Joyce jj@dbl.edu Barbara Richards Astronomy Galileo Galilei gg@pdv.it Preston Jones Astronomy Galileo Galilei gg@pdv.it Ryan Cooper Literature William Shakespeare ws@lu.ac.uk 352 Consider what would happen when the table has to be updated to reflect the following events: 1. Sandra Smith graduates. 2. Galilei s has changed 3. A new professor is hired and has to be assigned an office but has not yet been assigned any students to advise. Need proper design to avoid problems. Start with Conceptual Modeling

2 Handout 2 CS-605 Data Management and Systems Modeling Spring 18 Page 2 of 8 Key components: 1. Entity - Something of interest in the environment (e.g., person, place, object, event, concept) Must distinguish a concept of entity from that of an entity instance, which is a particular occurrence of an entity, e.g. Customer entity vs Scott George from Boulder, CO, which is an instance of Customer 2. Attribute - A characteristic (property) of an entity, which can be represented with a discrete (elementary) data element. 3. Identifier an attribute or set of attributes that is unique for every entity instance, i.e. no two entity instances can have the same value of the identifier attributes. 4. Relationship - an association between one or more entities. Illustrations: BOOK ISBN Title Price Publish Date AUTHOR Name Date of Birth ROYALTY CHECK Check No Check Date Check Amount PUBLISHER Pub Name Pub Mailing Address Pub Phone Publishes BOOK Book ISBN Book Title Book Price Book Nbr Pages Writes AUTHOR Author Name Author Address ROYALTY RATE - 2 -

3 Handout 2 CS-605 Data Management and Systems Modeling Spring 18 Page 3 of 8 Defining Entities An Entity SHOULD describe an object/concept that is important to business, that will have many instances in the database An Entity SHOULD NOT describe: A user of the database system An output of the database system (e.g. a report) Defining Attributes: Simple vs. Composite Simple - most basic level, non-decomposable Composite decomposable into a group of related attributes ex: Address (Street, City, State, Zip) Single Valued vs. Multi Valued Single - only one value per entity instance (e.g., last name, date of birth) Multivalued- multiple values per entity instance (e.g., degrees, clubs, skills) Shown in {}s, ex. {Degree} Stored vs Derived (e.g. DateOfBirth vs [Age] ) Identifier attribute (s) (e.g. SSN of a person) Used to uniquely identify every entity instance, i.e. no two entity instances can have the same value of the identifier attributes. Shown with underlining Can be natural or artificial - Create an identifier if there is no obvious identifying attribute (e.g., part number) Can be composed of multiple attributes, called, composite identifier - Consider substituting single-attribute identifiers in place of natural composite identifiers to simplify design and enhance performance. Preserve the natural identifier s uniqueness constraint. Should not change value over the lifetime of the object Intelligent identifiers (i.e. reflecting some meaning in a value) should be avoided, as the meaning can change. More on Entities and Identifiers: A WEAK entity will not have its own identifier, but will have a partial identifier attribute that must be combined with the identifier of its defining strong entity owner to create a full identifier. Partial identifiers of weak entities are shown with double underlining. An ASSOCIATIVE entity may or may not have its own identifier (examples later)

Handout 2 CS-605 Data Management and Systems Modeling Spring 18 Page 4 of 8 Defining Relationships A relationship is an association between one or more entities The degree of a relationship indicates

4 Handout 2 CS-605 Data Management and Systems Modeling Spring 18 Page 4 of 8 Defining Relationships A relationship is an association between one or more entities The degree of a relationship indicates the number of entities involved a) Unary (one entity type): b) Binary (two entity types): c) Ternary (three entity types): Different from a combination of three pairwise relationships: Doctor-Patient Patient-Med.Condition and Doctor-Med.Condition Often represented with an Associative entity

5 Handout 2 CS-605 Data Management and Systems Modeling Spring 18 Page 5 of 8 The cardinality of a relationship describes the number of instances of one entity associated with another entity. Broadly, for BINARY relationships, there are 3 categories 1. One-to-one 2. One-to-Many (many-to-one) 3. Many-to-Many Examples - 5 -

Handout 2 CS-605 Data Management and Systems Modeling Spring 18 Page 6 of 8 Relationships (many-to-many and one-to-one) can have attributes These attributes describe features pertaining to the

6 Handout 2 CS-605 Data Management and Systems Modeling Spring 18 Page 6 of 8 Relationships (many-to-many and one-to-one) can have attributes These attributes describe features pertaining to the association between the entities in the relationship A more refined specification: o Reflected via a minimum and a maximum number o Zero, one or many Entities can have more than one relationship between them (multiple relationships) - 6 -

7 Handout 2 CS-605 Data Management and Systems Modeling Spring 18 Page 7 of 8 Associative Entity = combination of relationship and entity, shown as rectangle with rounded corners. Some many-to-many relationships are better modeled as an Associative Entity. Especially useful when the entity instances has business meaning in its own right and participates in other relationships. (e.g. a Person s Diploma from a University) a) Many-to-many with attributes b) Associative entity without an identifier c) Associative entity with a partial identifier d) Associative entity with an identifier - 7 -

8 Handout 2 CS-605 Data Management and Systems Modeling Spring 18 Page 8 of 8 Practice problems: Create an ERD for each of the following situations. 1) Farmer Bob, Farmer Jane and Farmer Jose run a cow farming co-op. For every cow they keep the cow s name, age (or date of birth), breed and numbered plastic ear tag. Some of the cows belong to individual farmers, others are shared. 2) An art researcher has asked you to design a database to record details of artists and the museum in which their paintings are displayed. For each painting, the researcher wants to know the size of the canvas, year painted, title, and style. The nationality, date of birth and death of each artist must be recorded. For each museum, record details of its location and specialty, if it has one. 3) A hamburger shop makes several types of hamburgers, and the same ingredient can be used with several types of hamburgers. This does not literally mean the same piece of lettuce is used many times, but that lettuce is used with several types of hamburgers. 4) A country can have many official languages and a language can be the official language in many countries. Each language belongs to a language group. 5) You are working for a consulting company and want to create a database that will be used to track problems clients are having and the consultants who are working on them. Each client can have many problems and many clients can be facing the same problems. Each time a client reports a problem you want to track the client, what their problem is, the consultant who is working on it and the date it was logged into the system, its status and the date the problem was solved (note this is blank for pending problems). Consultants also work on many problems at any given time. For each type of problem there is one consultant who is considered the expert on this problem. A consultant can be an expert on many different types of problems

Represent entities and relations with diagrams

LEARNING OBJECTIVES Define data modeling terms Describe E-R Model Identify entities and relations Represent entities and relations with diagrams WHAT IS DATA MODELING? A data model is a collection of concepts