E-R Diagram Example. E-R Diagram for Everfail. Translating E-R Diagrams into Relations. The Complete Relations for EverFail. Car. Customer.

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1 Managing Data II Fundamentals of IT and E-Commerce Fall Session 3b Prof. Foster Provost Learning Objectives: Interpret and analyze a simple entity relationship diagram and validate its accuracy with respect to a given business description Translate a simple entity relationship diagram into a set of normalized relations, including the appropriate specification of foreign keys Describe the functionality of the basic relational algebra operators and be able to apply them using SQL Define the terms primary key, composite key, & foreign key Copyright IS MBA Core Faculty, E-R Exercise Attributes and Keys The Everfail company is in the quick oil and lube business. Although customers bring in their cars for what is described as "quick oil changes," Everfail also replaces windshield wipers, oil filters, and air filters, subject to customer approval. The invoice contains the charges for the oil used, all parts used, and a standard labor charge. Everfail's database is to be designed to keep track of all components in all transactions so that customers may be billed. Attributes: properties or characteristics of entities Attributes that uniquely identify an entity instance (i.e., row, record) are candidate keys Primary keys are the attributes chosen as the unique identifier to be used How to choose: should not change over time (age) must have unique, non-null values use as few attributes as possible Typically underlined (key) Employee EmpJob Emp EmpAddr 3 EmpID 4 1

2 E-R Diagram Example E-R Diagram for Everfail Cust ID Model Make VIN PartID Uses/ Invoice/Work Part Descr Part Price WorkID What s missing in this diagram that would be useful to specify? Work Workdescr LaborCharge 5 6 Translating E-R Diagrams into Relations VIN, Model, Make CustID,, Address, Phone ID, Workdescr, LaborCharge ID, PartDescr, PartPrice What s Missing? We haven t captured the relationships between the entities! We have no way of linking records across relations! 7 The Complete Relations for EverFail VIN, Model, Make, CustID CustID,, Address, Phone ID, Workdescr, LaborCharge, CustID ID, PartDescr, PartPrice Used ID, ID, Qty 8 2

3 Terminology: Another E-R Exercise (for practice) A Primary Key (or key) is an attribute, or group of attributes, that uniquely identifies a row in a relation. Every record must have a key. Often numeric. A Composite Key is a key that consists of two or more attributes. A Foreign Key is a non-key attribute in one relation that appears as the primary key in another relation. ABC bank is a small community bank servicing its customers through several branches in Hometown, USA. Each branch exclusively manages the accounts of its customers, although customers may transact business at any of the bank s branches. s can operate several different types of accounts: checking, savings, loan and investment. ABC bank requires a database system that tracks customer transactions with the bank and produces monthly statements summarizing account balances and transactions for the past month for each customer. 9 Getting information from a database How do you get various, aggregated information from these normalized tables? Query A question asked to a database, resulting in a virtual table as an answer Examples of a query SELECT Student_ FROM Student_Table WHERE major= MIS Query language Structured language for describing (precisely) the information needed from a database e.g. SQL (Structured Query Language) 4 th Generation Language -> language for users 11 Normalized Data Student Table Student ID# Class Table ID Student Title Intro. MIS Database Elec. Comm. Strategic MIS Telecomm Table Chatterjee Gilson Campus Address Teaching Assignment ID Location T240D T240E Term Phone Major Van Deventer Hann Chatterjee Chatterjee Gilson Phone Joy Egbert 100 N. State Street MIS Larry Mueller 123 S. State Street MIS Mike Guon 125 S. Elm MGT Jackie Judson 224 S. Sixth Street MKT Enrolled Table Student ID# ID Term Grade A B C+ A B C+ B A

4 Relational Algebra Structured Query Language Relational Algebra functions retrieve a subset of rows ( selection ) retrieve a subset of columns ( projection ) connect two relations (a join ) All relational DBMS will have commands that execute this functionality You can build any view of the data using these operators As the result of each operator is a view, a transient relation/table these can be nested (e.g., one query can produce a value needed for another query) Keys permit the application of relational Simple SQL query SELECT FROM WHERE relation-list A list of relation (table) names to work with (all necessary data in one of these tables), plus join information (see tutorial) target-list A list of attributes of relations in relationlist (these are the attributes of interest) qualification Comparisons ( Attr op constant or Attr1 op Attr2, where op is one of <, >, =,,, ) combined using AND, OR and NOT [DISTINCT] target-list relation-list qualification algebra operators across multiple tables Relational Database Relational Database s Last_name First_name Cust_ID Shipping_Address Phone_No. Uretsky Michael W. 23rd St., NY, NY, Davern Michael River Rd., Bell Harbor, NY Bernstein Abraham Mt. Pleasant Ave., Mamar Provost Foster Trump Tower, #54PH, NY, N SQL Query: SELECT FROM WHERE Returns: Last_name, Phone_No. s First_name = Michael Last_name Phone_No. Uretsky Davern s Last name First name C_ID Shipping Address Phone No. Uretsky Mike W. 23rd St., NY, NY, Davern Michael River Rd., Bell Harbor, NY Bernstein Abraham Mt. Pleasant Ave., Mamar Provost Foster Trump Tower, #54PH, NY, N Products P_ID Product_ Color Quantity Price 2728 Zenophone Silver Pilot VIII Black Ham Kit Silver Zenophone UpgrSilver Orders SQL Query: C_ID P_ID note: Oracle syntax SELECT Last_name, Phone_No. FROM s, Products, Orders WHERE (s.c_id = Orders.C_ID) and (Orders.P_ID = Products.P_ID) and (Price > 1000) 16 4

5 E-R Diagram Example E-R Diagram for Everfail Cust ID Model Make VIN PartID Uses/ Invoice/Work Part Descr Part Price WorkID What s missing in this diagram that would be useful to specify? Work Workdescr LaborCharge Translating E-R Diagrams into Relations VIN, Model, Make CustID,, Address, Phone ID, Workdescr, LaborCharge ID, PartDescr, PartPrice What s Missing? We haven t captured the relationships between the entities! We have no way of linking records across relations! 19 The Complete Relations for EverFail VIN, Model, Make, CustID CustID,, Address, Phone ID, Workdescr, LaborCharge, CustID ID, PartDescr, PartPrice Used ID, ID, Qty 20 5

6 E-R Diagram for ABC Bank CustID Relations for ABC Bank Branch BranchID BranchLoc TransID Date Amount Transactions Manages Comprise Operate Accounts Address Branch: BranchID, BranchLoc : CustID,, Address, BranchID Account: AccountNum, Type, OpenBal, CloseBal, CustID Transaction TransID, Date, Amount, AccountNum AccountNumber Type OpeningBal ClosingBal 22 6

Introduction to Database Systems

Introduction to Database Systems Introduction to Database Systems So, what is a database, anyway? An integrated, self-describing collection of data about related sets of things and the relationships among