UB MGS 351 - Test 2 REVIEW (21 pages)

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Test 2 REVIEW



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Test 2 REVIEW

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Pages:
21
School:
University at Buffalo, The State University of New York
Course:
Mgs 351 - Intro to Mgmt Info Systms

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MGS351 Review Sheet I Relational Database Design Relational Databases Store data in the form of related tables Relational design is based on database normalization and can be accomplished with ERD s Benefits o Ensures data integrity and referential integrity Adding deleting and updating records o Powerful to use Design Principles o You must become a business expert o Poor relational database design leads to system failure o Proper design accurately reflects the organization s business rules o Relational database design is both an art and science cost benefit Entity Relationship Diagrams diagramming tool used to design a relational database blueprint If designed properly an ERD will accurately reflect the business rules of the organization It will become a visual illustration of the organization s business rules Corrections are harder than adding on 1 1 1 N N M Entities rectangles Lines relationships Entity tables something about which data is kept Attribute fields descriptive value associated with an entity Key attribute primary keys attributes that uniquely identify an entity Example a customer entity has name address fax number and phone number attributes Relationships have 2 parts and an action verb to describe the process The concept of time must be factored into relationships Clearly define entities Identify all exceptions to the rule often difficult to define even if you are the business expert Transforming ERD s to Tables Entities tables Attributes fields Key attributes primary key Ensure all relationships simplify to a 1 N 1 1 1 relationships merge into one table One entity becomes an attribute of the other 2 1 N add a primary key from the one entity as a foreign key in the many entity 3 N M add an intersection table which includes a primary key from both tables Add intersection table Flip relationship lines around so the many side faces the intersection table Add primary keys from the original tables as fields in the intersection table use autonumber to create a new field or concatenate primary keys Assign a name to the intersection table Add other relevant fields to the intersection table if necessary See pages 7 8 for example Determining Relationships Every relationship is made of 2 halves To determine a relationship the correct questions must be asked o Can a single customer have one or many loans o Can a single loan be related to one or many customers o Can a single loan have one or many payments o Can a single payment be applied to one or many loans turn any M M or 1 1 into a 1 M relationships Database Normalization the way database design is often taught in classrooms The learning process of how to use relationships Application of a number of rules to the relational model which will simplify relationships o Avoid common database problems o Make the data as tightly bound as possible o Store the minimum amount of data First second and third normal form Un normalized vs Normalized Goal the fields in a table



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