Study Guide Mis 691 Chapter 2
Study Guide MIS 691 Midterm Chapter 2 2. 2 Entity: One affair or topic; article of accent to a user that needs to be represented in a database. In the entity-relationship model, entities are belted to things that can be represented by a distinct table. An archetype of this is in the EMPLOYEE table; abstracts about the article (the employee) is in the table rows and abstracts about the entity’s attributes are in the rows. 2. List the characteristics a table charge accept to be a relation: * Anniversary row of the table holds abstracts that affect to some article or a allocation of some article * Anniversary cavalcade contains abstracts of the attributes of the article * The beef charge authority a distinct value; no repeating elements * All of the entries in any cavalcade charge be the aforementioned affectionate * Anniversary cavalcade charge accept a different name and the cavalcade adjustment is unimportant * The adjustment of the rows in unimportant * No two rows in the table may authority identical abstracts ethics 2. 0 Define the appellation different key and accord an example: A key that defines a different row. An archetype of a different key in the EMPLOYEE table is EmployeeNumber; the concern of any EmployeeNumber (223 for example) will alone aftermath a distinct row and abstracts for one employee. 2. 11 Non-unique key: A key that potentially identifies added than one row. In the EMPLOYEE table from our book, Department is a non-unique key because it identifies several rows. 2. 12 Accord an archetype of a affiliation with a different blended key: A blended key contains two or added attributes.
An archetype of a different blended key in the EMPLOYEE table is if we accumulated LastName, FirstName, and Department as a key; these three attributes accumulated would assure that we would analyze alone one row. 2. 13 Explain the aberration amid a primary key and a applicant key: Applicant keys are keys that abnormally analyze anniversary row in a relation. They can be distinct or composite. The primary key is the applicant key that is called as the key that the DBMS will use to abnormally analyze anniversary row. 2. 5 What is a agent key and beneath what affairs would you use one? A agent key is a cavalcade with a unique, DBMS-assigned identifier that has been added to a table to be the primary key. You would use a agent key back the primary key in the table is not ideal. You add a agent because it is short, numeric, and will never change – it is an ideal primary key. 2. 20 Define the appellation referential candor abstemiousness and accord an example: A accord coercion on adopted key values.
A referential candor coercion specifies that the ethics of a adopted key charge be a able subset of the ethics of the primary key to which it refers. In the EMPLOYEE table: the amount of Department should bout a amount of DepartmentName in the DEPARTMENT table. 2. 21 Explain the three accessible interpretations of a absent value: 1. It could beggarly that no amount is adapted 2. It ability beggarly that the amount is accepted to be bare (intentionally larboard blank) 3. It may beggarly that the amount is alien 2. 4 Name the anatomic annex and analyze the determinants of: Area = Length x Width Area is functionally abased aloft Length and Width or that the blended of Length and Width are determinants of Area 2. 31 Describe the attributes and purpose of the normalization process: Normalization is breaking up tables with added than one affair into sets of tables that accept one affair each. You accept to do this so that there isn’t echo advice in a table and so there are no modification or abatement issues.
Normalization: Normalization is the action of breaking a table with one or added affair into a set of tables such that anniversary alone has one theme. You charge to actualize a admirable relation: 1. Every account charge be a applicant key 2. Any affiliation that is not admirable should be burst into two or added relations that are admirable The Normalization Process: 1. Indentify all of the applicant keys 2. Indentify all of the anatomic dependencies 3. Examine the dereminants of the anatomic dependencies.
If any account is not a applicant key, the affiliation is not well-formed. In this case: a. Place the columns of the anatomic annex in a new affiliation of their own b. Make the account of the anatomic dependacy the primary key of the new affiliation c. Leave a archetype of the determinat as a adopted key in the aboriginal affiliation d. Actualize a referential candor coercion amid the orginal and the new relation. 4. Echo footfall 3 until every key is a applicant key
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