I N T R O. Week 4 R E L A T I O N A L. Normalization D A T A B A S E S DPW

Transcription

1 Week 4 ormalization onna Warren

2 opics for this Unit ormalized data Update, delete, and insert problems First ormal Form (1F) econd ormal Form (2F) hird ormal Form (3F) elationship decompositions dvanced normalization forms When to stop normalizing onna Warren

3 What is ormalization? ormalization is the process of removing potential anomalies from the database design hese anomalies include: nsertion anomalies Update anomalies eletion anomalies educe the potential for anomalies during data operations mprove data consistency educe redundancy implify future extension of the logical data model onna Warren

4 onna Warren ample enormalized ata *note the duplicate entries

5 nsertion nomalies n insertion anomaly occurs when you can t enter a record because some data is missing Consider a database with the rule that every employee must be assigned to a project, but a newly hired employee doesn t have a project yet ne solution is to create a dummy project, but this puts bad data into your database and is not a good idea onna Warren

6 onna Warren nsert Problem

7 onna Warren eletion nomalies eletion anomalies occur when deleting a record accidently causes other data to be lost ook again at the table from the slide about insertion anomalies

8 onna Warren elete Problem

9 Update nomalies Update anomalies occur when the same data is stored in more than one place his means whenever you have to make a change to the data, you must do it in several places he more times you have to edit the same data in multiple places, the more chances you have of making a mistake, causing inconsistent data onna Warren

10 onna Warren Update Problem

11 onna Warren ata esigns

12 ormal Forms set of conditions on table structure that improves maintenance ormalization removes processing anomalies: Update nconsistent ata ddition eletion onna Warren

13 ormal Forms First ormal Form (1F) ll fields must contain single values econd ormal Form (2F) Part of the primary key may not determine a non-key field on-key attributes are fully dependent on the key hird ormal Form (3F) non-key field may not determine another non-key field onna Warren

14 ormal Forms oyce-codd ormal From (CF) very determinant is a key Much stricter 3F arely used in business Fourth ormal Form (4F) n an all-key table, part of the can determine multiple values of one other field arely used in business onna Warren

15 First ormal Form (1F) he First ormal Form involves getting rid of all repeating groups and arrays epeating groups can be lists of values separated by commas hey can also be enumerated fields such as phone1, phone2 etc lso, to meet 1F, every column should contain only one type of data onna Warren

16 lbum xample lbum racks rtist rtistcountry bby oad lond on lond Here comes the un, ctopus's Garden, omething, etc. ainy ay Woman, ad yed ady of the owlands, tuck in Memphis with the Mobile lues gain eatles ob ylan UK U onna Warren

17 lbum ist 1F he racks field in the lbum table is multivalued. t contains a list of the tracks associated with the album his violates 1F t is tempting to try to create a series of fields like rack1, rack2...rack13 his also violates 1F and is a bad idea for several reasons: What if there were 14 tracks? What if there were only 4? o find any 1 track, you would have to query 13 fields onna Warren

18 emporary olution lbums 1F lbumitle rack rtist rtistcountry bby oad Here Comes the un eatles UK bby oad ctopus's Garden eatles UK bby oad omething eatles UK lond on lond ainy ay Woman ob ylan lond on lond ad yed ady of the ob owlands ylan U U lond on lond tuck in Mobile with the Memphis lues gain ob ylan he tracks are no longer listed. ach is separated into individual rows. ach row is unique. till, there is a lot of redundancy U onna Warren

19 Contact ist xample 1 astame/ ept Firstame Phone uilding code uilding uilding ddress ble usan roadway dison 1700 roadway dmissions roadway dison 1700 roadway nderson lliot outh nnex 1650 roadway nderson Jolene outh nnex 1650 roadway radley isa roadway dison 1700 roadway rown Martin outh nnex 1650 roadway nformation echnology outh nnex 1650 roadway onna Warren

20 Contact ist Continued ffice ept ype tatus itle mail 314 HUM nstruction F Professor sable@university.edu 124 M 212 nstruction P Professor eanderson@university.edu 113 nstruction P Professor janderson@university.edu 114 M taff F Program ssistant, ab ssistant lbradley@university.edu 201 xempt ean mbrown@university.edu 200 onna Warren

21 onna Warren Contact ist xample 1F he contact spreadsheet has several problems: he astname/ept column stores two different types of values: employee names and department names lso some employees such as isa radley have more than one title

22 Contact ist olution he solution is to separate the epartment and astame into different columns he title we will break out into a separate ntity and then create a linking entity o do that we will need to provide primary keys. We will use a surrogate key for this example onna Warren

23 Contact ist ables 1F ContactKey astame Firstame eptame Phone 1 ble usan dmissions dmissions nderson lliot nderson Jolene radley isa rown Martin nformation echnology uilding code onna Warren

24 Contact ist Cont (1F) uilding roadway dison roadway dison outh nnex outh nnex roadway dison outh nnex outh nnex uilding ddress ffice ept ype tatus mail 1700 roadway 314 HUM nstruction F sable@university.edu 1700 roadway 124 M 1650 eanderson@university.ed roadway 212 nstruction P u 1650 roadway 113 nstruction P janderson@university.edu 1700 roadway 114 M taff F lbradley@university.edu 1650 roadway 201 xempt mbrown@university.edu 1650 roadway 200 onna Warren

25 itle and Contactitle ables itlekey itleame 1 Professor 2 Program ssistant 3 ean 4 ab ssistant ContactKey itlekey onna Warren

26 econd ormal Form (2F) econd ormal Form removes what are called functional dependencies Functional dependencies are groups of columns that depend on each other rather than on the key of the table ne way to look at functional dependencies is to look at them as themes or subthemes in the data onna Warren

27 lbum xample 2F n the lbum table, racks represent a separate theme or functional dependency rackitle, rtist and rtistcountry group together separate from the lbum rtist goes with track because many albums contain tracks by multiple artists We add primary keys to the lbum and rack tables onna Warren

28 lbum and rack ables (2F) lbumkey lbumitle bby oad lond on lond rackkey rackitle lbumkey rtist rtistcountry HC Here Comes the un eatles UK MH omething eatles UK PG ctopus s Garden eatles UK WM ainy ay Woman ob ylan Us ad yed ady of the ob ylan U owlands MM tuck in Memphis with the Mobile lues ob ylan U onna Warren

29 onna Warren lbum rack (2F)

30 Contact ist (2F) n the contact list, there are two distinct types of contacts: employees and departments uildingcode, uildingame and uildingddress also constitute a functional dependency he solution is to break both epartments and uildings into separate entities onna Warren

31 uilding & mployee ables 2F uildingkey uildingcode uildingame uildingddress roadway 1 dison 1700 roadway 1 outh nnex 1650 roadway mployeekey astame Firstame Phone uildingcode 1 ble usan nderson lliot nderson Jolene radley isa rown Martin ffice eptkey ype tatus mail nstruction F sable@university.edu nstruction P eanderson@university.edu nstruction P janderson@university.edu taff F lbradley@university.edu xempt mbrown@university.edu onna Warren

32 onna Warren epartment able 2F eptkey eptbrv eptame eptphone uildingcode ffice 1 Hum Humanities nformation echnology M Math M dmissions

33 onna Warren Contact ist 1F

34 onna Warren Contact ist 2F

35 onna Warren hird ormal Form 3F hird ormal Form removes more subtle dependencies called transient dependencies ransient dependencies are where a field depends more on another column for its meaning than on the able key

36 onna Warren lbum xample 3F n the lbum example, rtistcountry is a transient dependency t depends on rtistame more than on the rackkey he solution is to break rtistame and its dependent column rtistcountry into its own entity

37 lbumkey lbum ables 3F lbumitle bby oad lond on lond rtistkey rtistame rtistcountry eatles UK ob ylan U rackkey rackitle lbumkey rtistkey HC Here Comes the un MH omething PG ctopus s Garden WM ainy ay Woman ad yed ady of the owlands MM tuck in Memphis with the Mobile lues onna Warren

38 onna Warren lbum 3F

39 Contact ist 3F n the contact list example, two transitive dependencies exist n the mployee table, the room column depends on the uilding code he same dependency exists in the epartment table he solution is to create a new entity called uildingoom onna Warren

40 onna Warren ormal Form Violation Conditions hese are the conditions under with each type of violation can occur.

41 enormalization ometimes it is necessary to denormalize a table for performance reasons enormalization is where you recombine tables that were split apart to conform to the rules of the various normal forms enormalization should never be done lightly, because it opens up your database to the anomalies and errors normalization was designed to eliminate Goal of decomposition is to Preserve attributes (in a relation) Preserve dependencies e lossless which means we can get back to the normalized state using joins onna Warren

42 onna Warren enormalization Problems ata updates are less efficient because tables are larger ndexing is more cumbersome o simple strategies for creating virtual tables known as views

43 ormalization Process lso called ynthesis tart with attributes Combine them into groups Create the functional dependencies ormalize the data Create the normalized Map the to the schema When to stop normalizing - When applications require too many joins so performance suffers onna Warren

44 onna Warren ocumentation You should keep every version of your s as you work your way through the design and normalization process ach should contain notations about all changes and the reasons for making them

45 ata-modeling Checklist ata modeling translates specific realworld environment into data model epresents real-world data, users, processes, interactions ata-modeling checklist helps ensure that data-modeling tasks are successfully performed ased on concepts and tools learned in Part onna Warren

46 onna Warren

47 ummary able is in 2F when it is in 1F and contains no partial dependencies able is in 3F when it is in 2F and contains no transitive dependencies able that is not in 3F may be split into new tables until all of the tables meet 3F requirements ormalization is important part but only part of the design process onna Warren

48 ummary able in 3F may contain multivalued dependencies umerous null values or redundant data Convert 3F table to 4F by: plitting table to remove multivalued dependencies ables are sometimes denormalized to yield less /, which increases processing speed onna Warren

49 ummary ormalization can be tricky ome of the benefits of normalization include the following: Faster sorting and index creation larger number of clustered indexes arrower and more compact indexes Fewer indexes per table. his improves the performance of the, UP, and statements Fewer null values and less opportunity for inconsistency which increases database compactness onna Warren

50 onna Warren Video Modifying the omputing/shared_content/video/imprvn g_the_design.html

51 ab 2 - Part 1 fter reviewing your database design, the college has provided more information for the database that they want developed: For each student, the college needs to track the student, student names, addresses, start date, phone numbers and types (such as mobile, home, work), addresses and types (such as personal, school, work), gender, and birth date For each course, the college needs to track the course, course name, department, quarters offered, sections, and instructor teaching each course onna Warren

52 ab 2 Part 1 For each instructor, the college needs to track the instructor, name, address, phone numbers and types (such as mobile, home, work), addresses and types (such as personal, school, work), gender, birth date, and the courses that each instructor is qualified to teach dditionally, the college needs to track the final grades for each student after each course has completed. You need to modify your design and to reflect the new requirements onna Warren

53 ab 2 Part 2 Write a one to two (1-2) page paper in which you: 1. iscuss the degree to which you believe the Visio diagram reflects the database design 2. escribe any assumptions that you had to make about the business rules to in order to create the Visio diagram and the associated relationships onna Warren