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Database Management Systems

by: Laurianne White MD

Database Management Systems CSIS 350

Laurianne White MD

GPA 3.99

Evans Adams

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Evans Adams
Class Notes
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This 5 page Class Notes was uploaded by Laurianne White MD on Monday October 12, 2015. The Class Notes belongs to CSIS 350 at Fort Lewis College taught by Evans Adams in Fall. Since its upload, it has received 19 views. For similar materials see /class/221849/csis-350-fort-lewis-college in Computer Information Systems at Fort Lewis College.

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Date Created: 10/12/15
CSIS 350 Lecture 9 Read Chapter 3 pages 81 95 Homework On course web site Exam Results Mean 845 Median 8825 Max 98 Distribution lt70 1 70 7795 2 80 7 845 2 85 7 895 5 90 7945 2 95 2 Discuss first problem 3 types of database design design from existing data spreadsheets reports etc design new database database redesign 7 combine databases or database extracts Hierarchical Network and Relational are DB models Point here I may not have talked about this in class very much but I assigned it as part of the reading I expect you to actually read the material Chapter 3 Evans discussed Functional Dependencies Let s do a quick review Relation see slide 1 Functional Dependency One attribute or set of attributes determines the values of another attribute or set of attributes Determinant Attributes on left side of FD is called the determinant Composite Functional Dependencies Composite determinant Warning sample data may not be sufficient to determine functional dependencies May need to ask experts specific questions May need to use your intuition Keys A key is a combination of one or more columns that is used to identify particular rows in a relation A key with more than one column is called a composite key A candidate key is a determinant that determines all other columns in a relation When designing database tables one of the candidate keys is selected as the primary key This DBMS uses the primary key as its preferred method for nding rows in a table A surrogate key is an arti cial column that is added to a table to serve as a primary key A foreign key is a column or composite in one table that is the primary key in a second table referential integrity constraint a statement that limits the values of a foreign key Typically it says that the value of the foreign key must already eXist in the table that the key refers to Modi cation Anomalies Deletion anomaly deleting a row in a table causes it to lose facts about more than one thing Insertion anomaly inserting rows in a table can lead to inconsistent data because rows contain duplicate information Update anomaly changing data in a row may lead to inconsistent data Normal Forms A normal form is a way to organize relations so that they have certain properties Any table that meets the de nitions of a relation is in rst normal form 1NF 2NF All nonkey attributes are functionally dependent on the entire key no partial dependencies If key is composed of single attribute then relation is automatically 2NF 3NF Relation is 2NF and has no transitive dependencies BCNF BoyceCodd NF Every determinant is a candidate key A table in BCNF has no modi cation anomalies due to functional dependencies 4NF BCNF plus no multivalued dependencies No modi cation anomalies due to multivalued dependencies DKNF domain key NF no modi cation anomalies of any type Each normal form is more restrictive than the one before it so something that is in 3NF is automatically 2NF 3NF and BCNF are most important forms in practice Examples lNF but not 2NF ART200 22234 TRlO ART25 C Anomalies Can t insert a new student until heshe registers for a class Can t schedule a class until there are students If we delete a class we might delete all information about a student Key ClassNo StuID Partial Dependency StuID 9 LastName 2NF but not 3NF Student Table Anomaly Can39t insert information about number of credits required to be a Sophomore until we have at least one student in that category 2NF nonkey attributes functionally dependent on entire key 3NF no transitive FDs Key StuID FD StuID 9 LastName Major Credits Status FD Credits 9 Status So transitively StuID 9 Credits 9 Status 3NF but not BCNF Facult Table FacName I Dept I Of ce I Rank I HireDate Manatee Assumptions Prof names unique within department Profs have only one office Departments may have multiple offices and faculty may share offices FDs office 9 dept facName Dept 9 Office Rank HireDate facname Office 9 Dept Rank HireDate Choose facName dept as key 3NF Nonkey attributes FD on entire key 2NF plus no transitive anomalies BCNF 3NF plus every determinant is a candidate key Table is 3NF but not BCNF In this case the determinant office is not a candidate key Eliminating Anomalies Most modification anomalies are due to problems associated with func dependencies Can avoid this problem by designing tables in BCNF every determinant is a candidate key Normalization is a process of evaluating and converting a relation to reduce modification anomalies Essentially normalization detects and eliminates data redundancy Anomalies can be removed by splitting the relation into two or more relations each with a d erent single theme However breaking up a relation may create referential integrity constraints Procedure for converting relation to BCNF Identify every FD 2 Identify every candidate key 3 if there is a FD whose determinant is not a candidate key choose the one with the most columns and a Move the columns of that FD to a new relation b Make the determinant of that FD the primary key of the new relation V c Leave a copy of the determinant in the original table as a FK d Create a referential integrity constraint between the original and new relations 4 Repeat step 3 as needed Try this on the example tables Class Table create new tables Register classNo StuID Grade Student stuID Lastname Class2 ClassNo FacID Schedule Room Ref Integrity constraints Register StuID must exist in Student StuID Register classNo must exist in Class2classNo Student Table create new tables Student2 StuID LastName Major credits ClassRank Credits Status Ref Integrity constraints Faculty Table create new tables DeptOfficeOff1ce Dept Fac2 FacName Office Rank HireDate Ref Integrity constraint DeptOfficeO ice must exist in Fac20ffice


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