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... firm perform a job such as decorating a new home, redecorating rooms, locating ... several repairs (e.g., replacing the left fender, painting the passenger door) ...
Title: Announcements 1 Announcements
  • Reading for Wednesday
  • 3.5 3.9
  • Homework 2 - Due 9/22
  • Select paper topic and email me your choice
  • 2 The Entity-Relationship Model Entities, Attributes, and Keys
  • Lecture 5
  • 3 Purpose of E-R Model
  • 4 Symbols used in E-R Diagram
  • Entity rectangle
  • Attribute oval
  • Relationship diamond
  • Link - line
  • 5 Entity
  • Object that exists and that can be distinguished from other objects
  • Can be person, place, event, object, concept in the real world
  • Can be physical object or abstraction
  • In E-R diagram, rectangle represents entity set
  • 6 Entity Vocabulary
  • Entity instance is a particular person, place, etc.
  • Entity type is a category of entities
  • Entity set is a collection of entities of same type
  • Entity set must be well-defined
  • 7 Attributes
  • Domain
  • 8 Attribute Variations
  • May have null values for some entity instances
  • May be multi-valued
  • May be composite
  • May be derived
  • 9 Keys
  • Superkey
  • Composite key
  • Candidate key
  • Primary key
  • 10 More Keys
  • Alternate key
  • Secondary key
  • Foreign key term used in relational model (but not in the E-R model) for an attribute that is primary key of a table and is used to establish a relationship, usually with another table, where it appears as an attribute also
  • 11 Recognizing Entities, Attributes, and Keys
  • A dentists office needs to keep information about patients, the number of visits they make to the office, work that must be preformed, procedures preformed during the visit, charges and payments for the treatment, and laboratory supplies and services. Assume there is only one dentist, so there is no need to store information about the dentist in the database. There are several hundred patients. Patients make many visits, and the database should store information about the services performed during each visit, and the charges for each of the services. there is a standard list of charges, kept outside of the database. The office uses three dental laboratories that provides supplies and services, such as fabricating dentures.
  • 12 (No Transcript) 13 Recognizing Entities, Attributes, and Keys
  • An interior design firm would like to have a database to represent its operations. A client (customer) requests that the firm perform a job such as decorating a new home, redecorating rooms, locating and purchasing furniture, and so forth. One of the firms decorators is placed in charge of each job. For each job, the firm provides an estimate of the amount of time and money required for the entire job. Some of the work for a job, such as planning furniture placement, is done by the decorator in charge of the job. In addition, the firm might hire contractors to work on a daily or hourly basis on a particular job. A job might also include several activities, such as painting, installing floor covering, fabricating draperies, wallpapering, constructing, installing cabinets, and so on. These activities are done by contractors hired by the firm .The contractor provides an estimate for each activity. An activity or job might also require materials such as paint or lumber, and the firm has to keep track of the cost of materials for each activity or job, in order to bill the client. The database should store the estimated costs of all activities and all jobs.
  • 14 (No Transcript) 15 Recognizing Entities, Attributes, and Keys
  • An automobile body repair shop needs to keep information about its operations. Customers initially bring their cars to the shop for an estimate of the repairs. A mechanic looks at the car and estimates the cost and time required for the entire job. If the customer accepts the estimate, a job number is assigned and the customers name and contact information the cars license plate number, make, model, and year and a list of repairs needed is recorded. The customer than makes an appointment to bring in the car on a specified date. When the car is brought in for repairs, the work begins. The shop keeps track of the charges for the parts and labor as they accumulate. Only one mechanic works on the car for the entire job. A job might include several repairs (e.g., replacing the left fender, painting the passenger door). The time actually spent for each repair is recorded and used to calculate the cost of labor, using a fixed hourly rate.
  • 16 (No Transcript)
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