Entity Relationship Diagrams and Relational DBs

Transcription

1 Entity Relationship Diagrams and Relational DBs BSAD 4 Dave Novak Topics Covered ERD (entity relationship diagram) Data Modeling Entity vs- Entity set Attribute vs- Relationship Types of attributes and their domain Characteristics of relationships Degree Connectivity Existence Modeling Modeling Why would it be necessary or useful to model the structure of a database system? Before spending time and money on implementation: Make sure structure of DB is logical and technically correct Make sure structure addresses needs and constraints of data collection and use Make sure structure helps supports organization s information needs Data Model Entity-Relationship Diagram (ERD) Popular model that focuses on data ERD ERD: Graphical blueprint for the exact design and structure of a relational DB Shows details of things organization collects data about and how those things are related Relational Database Management System RDBMS A very popular, widely used DBMS Made possible by modern computing power computer must a lot of processing work User does not need to understand the underlying structure of the database Based on SQL

2 Organization of data in two-dimensional tables connected via relationships Tables are linked to one another using a common data element (attribute) that appears in both tables By linking tables via relationships users can navigate the database and extract and combine data from different tables The Table is the fundamental component in a relational database All data belong to a table This approach provides a much easier way to manage data Data are essentially grouped by common themes and then connected by relationships in a logical manner based on the ERD A relationship is a connection between two or more simple two-dimensional tables that consist of rows (entity / records) and columns (attributes / fields) of data Each entity is a unique observation Each row in a table Attributes are the common characteristics that are used to describe the entities in the table The columns in each table Power of an RDBs comes from ability to quickly find and bring together data stored in separate tables using queries, forms, and reports Can bring together attributes and entities from separate tables CLASS SECTION Table Course Max Current Start End Time CRN Dept # Title Sec Enroll Enroll Time Days InstructoCredits T R Jones BSAD 20 Prin Mgmt & Org Behavior A :30 0: BSAD 20 Prin Mgmt & Org Behavior B 40 4 :00 2:5 T R Jones BSAD 20 Prin Mgmt & Org Behavior C :00 20:00 R Viets BSAD 20 Prin Mgmt & Org Behavior D :05 :50 F Viets BSAD 20 Prin Mgmt & Org Behavior E :20 5:00 F Viets BSAD 2 ST: Human Resources Mgmt B :35 6:50 M W McIntosh BSAD 32 Legal & Political Envir of Bus A :00 5:5 T R Monte BSAD 32 Legal & Political Envir of Bus B :30 6:45 T R Monte BSAD 4 Mgmt Information Systems A :05 0:20 M W Kraushaa BSAD 4 Mgmt Information Systems B :35 :50 M W Kraushaa BSAD 4 Mgmt Information Systems C :35 6:50 M W Novak BSAD 42 Structured Business Prgmming A 40 9 :00 2:5 T R Bovee BSAD 43 Struc Anyl & Dsgn Business Sys A :00 8:5 M W Kraushaa BSAD 46 Loc Area Net/Wrk Grp & Sm Bus A 40 0:35 :50 M W Novak BSAD 50 Marketing Management A :00 5:5 M W Zhang BSAD 50 Marketing Management B :30 3:45 T R Noordew BSAD 50 Marketing Management C :00 5:5 T R Noordew 3 2

3 Review Review Key Terminology EMPLOYEES IN A DEPARTMENT EMPLOYEE_ID NAME SALARY POSITION... A09 Jane Adams 45, Computer Associate F04 Kent Fuller 34, Executive Secretary L002 LeAnn Lynn 56,29.00 Lab Manager What is the entity set represented here? What is an example of an entity within the entity set? What are some of the attributes of the entity? Why is the first field Employee ID underlined? Entity Set / Table (has a name that directly relates to the primary information stored in the table) Entity / Record (this is a row in a table) Attribute / Field (this is a column in the table that describes a characteristic of the entity) Relationship (an association or linkage between two (+) tables) Primary Keys Each record/entity must have a attribute (field/column) or set of attributes that uniquely identifies that specific entity from all the other entities stored in the table The unique attribute (or set of attributes) is called the primary key Primary Keys For our purposes: ALL relational DB tables must have a primary key ALL entities within the table must have a unique primary key value The primary can be created by you Doesn t have to provide value-added information Can be a combination of fields/attributes Can be sequential numbers Can be a combination of letters and numbers Cannot be repeated or left blank for an entity Different Types of Attributes Simple vs- composite Single valued vs- multi-valued Attribute Domain The collection or range of all possible allowable values an attribute may take on EmpDOB: list of all valid employee birth NumDependents: positive integers from 0 to 5 Height: positive real numbers between 36.0 and 84.0 inches. UnionMember: logical yes (true) or no (false) EmpSSN: list of valid social security numbers 3

4 Value for Each Attribute Each data attribute takes on a specific value: A value is one particular instance of an allowable attribute for an entity e.g. Employee attributes: Relationships Entities are connected to one another via relationships The association between two or more entities How we connect the entities or rows in one table to the entities or rows in another table EmpSSN EmpDOB NumDependents Unionmember Height Relationships 3 important characteristics of relationships: ) Degree 2) Connectivity 3) Existence Relationship Degree Loosely equal to the number of entities involved in a particular relationship Could also view this more simplistically as the number of tables linked by each relationship = Unary (aka recursive) 2= Binary 3= Ternary Three types of connectivity relationships are used to describe associations between the entities in different tables How are entities logically connected in the DB? ) One-to-Many 2) Many-to-Many 3) One-to-One Why does this matter? Logically the relationship needs to make sense Don t want the database functionality to allow relationships that are not feasible or practical From a practical perspective, the foreign key always goes on the many side of the relationship need to get this correct Special implementation of M:M & : 4

5 Employee Employee # Employee #2 Employee #3 : Vehicle Company Vehicle # Company Vehicle #2 Company Vehicle #3 This relationship connectivity shows that each employee can be associated with only one company vehicle and that each company vehicle can be associated with only one employee. One-to-One relationship Employee is assigned to one Company Car Each Company Car is assigned to only one employee In this case, the RDB will be structured in a manner that matches a specific employee to a specific company car each and every day. Each car would be explicitly linked to a particular employee Employee Employee # Employee #2 Employee #3 Employee #4 :M Accounting Human Resources Dept This relationship connectivity shows that each employee can be associated with only one organizational department (employees cannot simultaneously be assigned to, or work in, two different departments). However, each department can be staffed with many / multiple employees M One-to-Many relationship A professor can teach many different class sections Each class section is taught by only one professor A customer account can contain many invoices Each invoice is associated with only one customer account One-to-Many example Relationship is labeled :M Professor Each teaches M Each is taught by Class Section Read: left to right on the top of the line Read: right to left on the bottom of the line Customer Customer # Customer #2 Customer #3 M:M # #2 #3 #4 This relationship connectivity shows that customer can be associated with many different products and that each product can be associated with many different customers This relationship will be modeled in a special way!! M M 5

6 Many-to-Many relationship Employee has many job skills Each job skill can be learned by many employees Student can take many class section Each class section can be taken by many students Relationship Existence Denotes whether participation in a relationship is required (or not), and the minimum and maximum number of entities that participate in a particular relationship Mandatory: The existence of one entity depends on the existence of another entity Optional: The existence of one entity is independent of the existence of another entity Mandatory Relationship Existence Example Optional Relationship Existence Example Employee :M Employee :M Employee # Accounting Employee # Accounting Employee #2 Employee #3 Human Resources Dept Employee #2 Employee #3 Human Resources Dept Employee #4 Employee #4 The existence of an instance of employee (an individual employee) depends on the existence of a department where the employee will be assigned In this case, the entity set will need to be populated before the entity set Employee is populated The existence of an instance of employee (an individual employee) is independent of the existence of a department where the employee will be assigned In this case, the entity instance employee #4 can be created without the need to assign that employee to a department Relationship Existence Example Discuss :M Course Section CRN 5099 CRN 5060 CRN 506 CRN 5062 Course BSAD 4 BSAD 73 BSAD 20 Investigating Relationships :M relationship This relationship states that each supplier can provide (or distributes) many different products (, 2, n), but each of those products is provided by (or distributed by) only one supplier In this case, the structure would not allow a specific product to be provided by (or distributed by) to more than one supplier Can provide M Is provided by 6

7 Investigating Relationships :M relationship Table Can provide M Is provided by Nike produces and distributes many models of shoe that are unique to Nike Adidas produces and distributes many models of shoe that are unique to Adidas ASICS produces and distributes many models of shoe that are unique to ASICS ID Company Name Contact Name Contact Title Address City Region Postal Code Country Phone New Orleans Order P.O. Box New (00) Cajun Delights Shelley Burke Administrator Orleans LA 707 USA 4822 Grandma Kelly's Sales (33) Homestead Regina Murphy Representative 707 Oxford Rd. Ann Arbor MI 4804 USA th Bigfoot Regional Avenue (503) Breweries Cheryl Saylor Account Rep. Suite 20 Bend OR 970 USA 993 Can provide M Is provided by Table Can provide M Is provided by Units Quantity Unit Units In On Reorder ID Name ID Category Per Unit Price Stock Order Level Uncle Bob's Organic Dried 2 - lb 7 Pears 3 Seafood pkgs. $ Northwoods Cranberry 2-2 oz 8 Sauce 3 s jars $ Chef Anton's Cajun 48-6 oz 4 Seasoning 2 s jars $ Chef Anton's 5 Gumbo Mix 2 s 36 boxes $ Beverages bottles $ Sasquatch Ale 6 bottles $ Steeleye Stout 6 Beverages Louisiana Fiery Hot Pepper 32-8 oz 65 Sauce 2 s bottles $ Louisiana Hot 24-8 oz 66 Spiced Okra 2 s jars $ Table ID Name ID Category Uncle Bob's Organic Dried Pears 3 Seafood Northwoods Cranberry Sauce 3 Chef Anton's Cajun Seasoning 2 Chef Anton's Gumbo Mix 2 s s 34 Sasquatch Ale 6 Beverages 35 Steeleye Stout 6 Beverages Louisiana Fiery Hot Pepper Sauce 2 Louisiana Hot Spiced Okra 2 Quantity Per Unit Unit Price Units In Stock Units On Order Reorder Level 2 - lb pkgs. $ oz jars $ oz jars $ s 36 boxes $ s s bottles $ bottles $ oz bottles $ oz jars $ Notice that ID is not an attribute of it is the PK of the table and will be the FK (to the table) in the table ID Company Name Contact Name Contact Title Address City Region Postal Code Country Phone New Orleans Order P.O. Box New (00) Cajun Delights Shelley Burke Administrator Orleans LA 707 USA 4822 Grandma Kelly's Sales (33) Homestead Regina Murphy Representative 707 Oxford Rd. Ann Arbor MI 4804 USA th Bigfoot Regional Avenue (503) Breweries Cheryl Saylor Account Rep. Suite 20 Bend OR 970 USA 993 Units Quantity Unit Units In On Reorder ID Name ID Category Per Unit Price Stock Order Level Uncle Bob's Organic Dried 2 - lb 7 Pears 3 Seafood pkgs. $ Northwoods Cranberry 2-2 oz 8 Sauce 3 s jars $ Chef Anton's Cajun 48-6 oz 4 Seasoning 2 s jars $ Chef Anton's 5 Gumbo Mix 2 s 36 boxes $ Beverages bottles $ Sasquatch Ale 6 bottles $ Steeleye Stout 6 Beverages Louisiana Fiery Hot Pepper 32-8 oz 65 Sauce 2 s bottles $ Louisiana Hot 24-8 oz 66 Spiced Okra 2 s jars $ Investigating Relationships The :M relationship example The ID attribute in the table is a foreign key that links the individual products in the table to a specific supplier in the table 7

8 Summary. Describe the differences between ERDs and DFDs 2. Describe importance of relational DBs 3. Familiar with all terminology: tables, relationships, entities, attributes, keys, etc 4. Understand how to implement a relationship 5. Discuss / define the 3 characteristics of relationships 8