Study Guide Mis 691 Chapter 2

Study Guide MIS 691 Midterm Chapter 2 2. 2 Entity One theme or topic both(prenominal)thing of importance to a substance abuser that needs to be represented in a database. In the entity-relationship model, entities ar curtail to things that tail assembly be represented by a sensation disconcert. An manikin of this is in the EMPLOYEE put off data about the entity (the employee) is in the table quarrels and data about the entitys attributes are in the rows. 2. List the characteristics a table must have to be a relation * Each row of the table holds data that pertain to whatever entity or a portion of some entity * Each towboat contains data of the attributes of the entity * The cells must hold a single evaluate no repeating elements * All of the entries in any column must be the same kind * Each column must have a quaint name and the column order is piddling * The order of the rows in unimportant * No devil rows in the table may hold identical data determine 2. 0 Defin e the term whimsical winder and give an vitrine A chance on that defines a unique row. An example of a unique distinguish in the EMPLOYEE table is EmployeeNumber the query of any EmployeeNumber (223 for example) aloneow for but produce a single row and data for peerless employee. 2. 11 Non-unique reveal A call that potentially identifies to a greater extent than champion row. In the EMPLOYEE table from our book, discussion section is a non-unique chance on because it identifies some(prenominal) rows. 2. 12 Give an example of a relation with a unique involved mainstay A composite key contains two or more attributes.An example of a unique composite key in the EMPLOYEE table is if we combined Last discover, FirstName, and Department as a key these trinity attributes combined would insure that we would identify merely unity row. 2. 13 Explain the contrariety between a radical key and a medical prognosis key panorama keys are keys that uniquely identify all(preno minal) row in a relation. They can be single or composite. The primary key is the candidate key that is elect as the key that the DBMS exit use to uniquely identify severally row. 2. 5 What is a surrogate key and under what circumstances would you use one? A surrogate key is a column with a unique, DBMS-assigned identifier that has been gibeed to a table to be the primary key. You would use a surrogate key when the primary key in the table is non ideal. You add a surrogate because it is short, numeric, and will neer change it is an ideal primary key. 2. 20 Define the term referential fair play restraint and give an example A relationship diffidence on outside key values.A referential integrity control specifies that the values of a foreign key must be a veracious subset of the values of the primary key to which it refers. In the EMPLOYEE table the value of Department should equip a value of DepartmentName in the section table. 2. 21 Explain the three potential interpret ations of a null value 1. It could cerebrate that no value is appropriate 2. It skill symbolize that the value is known to be blank (intentionally left blank) 3. It may mean that the value is unknown 2. 4 Name the utilitarian dependency and identify the antigenic determiners of part = Length x largeness country is functionally dependent upon Length and largeness or that the composite of Length and Width are determinants of Area 2. 31 limn the nature and purpose of the normalization plow Normalization is breaking up tables with more than one theme into sets of tables that have one theme each. You have to do this so that there isnt repeat cultivation in a table and so there are no adaptation or deletion issues.Normalization Normalization is the mental process of breaking a table with one or more theme into a set of tables such that each only has one theme. You need to create a well-formed relation 1. Every determinant must be a candidate key 2. Any relation that is non w ell-formed should be broken into two or more relations that are well-formed The Normalization Process 1. Indentify all of the candidate keys 2. Indentify all of the functional dependencies 3. attend the dereminants of the functional dependencies.If any determinant is not a candidate key, the relation is not well-formed. In this case a. Place the columns of the functional dependency in a new-fangledborn relation of their own b. Make the determinant of the functional dependacy the primary key of the new relation c. Leave a imitation of the determinat as a foreign key in the original relation d. realize a referential integrity constraint between the orginal and the new relation. 4. Repeat trample 3 until every key is a candidate key