DATABASE DESIGN

ERD Entity Relational Diagram (ERD) Visual display of tables and their relationships for a database Used for “Relational Modeling” 2

ERD cont. SQUARES indicate TABLES LINES between them indicate the different relationships “FEET” at end of line, indicates a “MANY” relationship -1 CUSTOMER has MANY “receipts” -1 STAFF MEMBER sells MANY “receipts” -1 PRODUCT can go into many different “receipts” Each product has to be INDIVIDUALLY listed 3

ERD cont. IF I wanted to know who sold me the order, I have to go to the receipt (order ), in the “RECEIPT” table, I’ll find who the STAFF MEMBER is who sold me that receipt IF I wanted to know what product a CUSTOMER has ordered, I have to go to the receipt (order ), in the “ PRODUCT” table -NO DIRECT relationship BETWEEN : CUSTOMER & STAFF, or CUSTOMER & PRODUCT 4

What are Tables or Entities Used to represent things in the “real world” that is of significant interest to the user i.e. “EMPLOYEES” might be an “Entity” in a company database NOUNS in a “Business Narrative” each table is called an “entity” and the columns are referred to as an “attribute”. within a table, each row is called a “record” and it represents 1 particular instance of its “entity” (not unlike the flat file). 5 Employees

Entities Continued Another example: A database regarding music Artist & Song are both tables “Performs” is the relationship (VERB) (usually is a “supporting document” which explains the relationship) 6

Entities and Their Attributes “Entities” represent something of importance “Entities” are made up of several “Attributes” (the columns), which describe the tables: 7 ARTISTS ArtistName Gender SONGS SongTitle Length

Entities Summarized Each ENTITY is made up of rows and columns Columns are called fields or attributes of a database Rows are called records or an instance of an entity If you have repetitive VALUES to 1 attribute, —create a: “JOINER TABLE” or “LOOKUP TABLE” make this attribute a “Foreign” key Create another table with same attribute i.e. a: “Shoe Table” with “colours” “Colours” will be a “Foreign” key, here: with “ColourID” primary key in a new table called: colours, with “ ColourID ” 8-10 attributes per TABLE, after that create another table 8

Entities Summarized cont. OR: When a table has the SAME VALUE REPETITIVELY for that attribute, you might need a “LOOKUP TABLE”: 1. People might misspell, the value, then you can’t do a: SEARCH  i.e. LEVEL OF EDUCATION  “Masters”  What if 1 person spells it: “Masters” o Another person “Master” o Another person Masters of Education 2.You will have multiple occurences of 1 VALUE which takes up too much space in your database 9

Steps in Database Design 1.Complete a “Needs Assessment” (note: this is a huge process that is not covered in this course) Basically, you speak with end users, managers, existing documents and think “outside the box” If, in the design of the database, there is multiple occurrences of data (think of our “gender” example) this is an indicator that another table should be created. 2.Create a “Business Narrative” 3.Identify entities 4.Identify attributes & keys 5.Identify relationships 10

Business Narrative Vital link between database designer and the end users Purpose is to make clear the “data requirements” The story, business rules, purposes of database; what kind of info it will hold Will have to go over the DESIGN multiple times/days to make sure the DESIGN is correct Get other people/users to comment on design Example: “Algonquin college employs many instructors to deliver various programs comprised of many different courses. “ 11

Starting an ERD Identify the “entities” Look at NOUNS of the “Business Narrative” “Algonquin college employs many instructors to deliver various programs comprised of many different courses.” 12 instructors programs courses

When the list of Entities Seems Complete Ask about each “entity”: 1.Is it significant? List only entities that are important to your database users and that are worth the trouble and expense of computer tabulation. 2.Is it generic? List only types of things, not individual instances “EMPLOYEES”, “INSTRUCTORS” are generic of many different instances—we don’t say “Joe” 3.Is it fundamental? List only entities that exist independently and do not need something else to explain them. “Courses”-explains itself, you don’t need further elaboration 13

RELATIONSHIPS

Three Basic Types of Relationships One to One (1:1) One to Many (1:M) Many to Many (M:M) The 1 is the “PARENT”, and the M is the “CHILD” Called the CARDINALITY of the relationship The cardinality indicates the MAXIMUM number of RELATIONSHIPS between the entities, Whenever you see: “MANY”—this will be the FOREIGN KEY

One to One Relationships 1:1 relationships exists when a single record in one table has 1 and only 1 corresponding record in another table, and vice versa VERY RARE When you created a table for something, when it really should only have been a “field” The 1 should really have been an “attribute” of the other (table/entity) an attribute IMPROPERLY DEFINED as an entity i.e. 1 customer, 1 address “Address” should have been the attribute of the “Customer” table

One to One Example A voter can cast only one vote in an election. A ballot paper can belong to only one voter. So there will be a 1:1 relationship between a Voter and a Ballot Paper. Voter Ballot

One to Many Relationships MOST COMMON 1:M or M:1 Relationship exists when a record can relate to 1 OR MORE records in a 2nd table but.. A record in the 2nd table can ONLY relate to 1 record in the 1st table

One to Many Example A person can own more than one car. A car can only have one owner. OwnerVehicle

Many to Many Relationships M:M Relationship exists when 1 record in either table can relate to more than 1 record in the other table These should be eliminated 2 related “PARENT” tables, but their relationship is NOT “direct” Instead, it needs to be related through an additional “CHILD” table

Many to Many Example A student can have more than one professor; the same professor can have many students WATCH THIS VIDEO StudentProfessor

Resolving Many to Many M:M is not allowed, as an attribute could have more than 1 value: A “Multi-Valued Attribute” Difficult to generate reports, or do searches Would have to repeat attributes multiple times Instead, we create a “JUNCTION” or “JOINER ENTITY” The name of the joiner entity is often a COMBINATION of the 2 entities StudentProfessorStud_Prof

Many to Many Relationships

Resolving Many to Many Relationships By Creating A Junction Or Joiner Entity WATCH THIS VIDEO

SHEETS OF ICE 1 arena with many sheets ARENA ID-primary key in ARENA table Add a FOREIGN KEY to SHEETS OF ICE ( AREN_AID) Can a sheets of ice belong to many arenas?NO—so we know it’s a one-to-many TEAMS table-PRIMARY KEY: TEAM ID to PLAYERS table FOREIGN KEY: TEAM ID

Relationship Review

Normalization Refining the ERD Task of analyzing entities and the relationships created have been formalized into a process called normalization. Should resolve all your relationships to One to Many (1:M) relationships Eliminate all One to One’s (1:1) and Many to Many’s (M:M)

Selecting Attributes Attributes are the fields/columns that describe an entity Attributes can be: A Characteristic A Quality A Feature A Fact An attribute is a “non-decomposable” piece of information about an entity Can’t be broken down any further, only 1 single value per column i.e. NAME—last name, 1 st name Attribute “Naming Conventions” Single word (or more than 1 word with an underscore (no spaces) Unique Can’t be a reserved word” i.e. “Number”, “Date” ( these are date types), OR name of column can’t be same as name of table 28

ONLY WATCH UNTIL 5 minutes 31 seconds (until it mentions: “QUERYSMITH”) Y-bvjtYgRVU Y-bvjtYgRVU 29

RULES DEFINING TABLES, ROWS, AND COLUMNS 30

Rule Columns must stand alone The order of columns within a table has no meaning in the model The model should still be correct even if the columns are rearranged 31

Rule Columns must have a unique name Column values must be “unitary” Only 1 value possible, i.e. only 1 “square footage” A Column can contain only SINGLE values, never lists For example if you decide to treat a person’s first and last names as separate values, the names must be in separate columns not in a single Name column 32

Rule Each column must contain data of a single type i.e. dates, number, text Rows must be unique In every row, some column must contain a unique value 33

Rule Rows must stand alone Each row of a table is independent and does not depend on any other row of the same table. As a consequence, the order of the rows in a table is NOT significant 34

Review Tables / Entities Tables (aka Entities) in the relational model are used to represent “things” in the real world. Entities are made up of attributes Attributes (columns/fields) are pieces of data that describe the entity Rows are called records Primary Key Foreign Key 35

myitlab

ASSIGNMENTS-BE CAREFUL WHEN DOWNLOADING “CHEATING” possibilities BE CAREFUL when you are DOWNLOADING your assignment files. When you DOWNLOAD them, the files come with an embedded ENCRYPTION code IF you COPY THE FILE from another student, your assignment will be flagged with a “POTENTIAL INTEGRITY VIOLATION”,(cheating). EVEN IF YOU SEND AN UN edited file, you may be legitimately doing your own work, but, the file has the ENCRYPTION code your assignment will be flagged with a “POTENTIAL INTEGRITY VIOLATION”, (cheating). 37

ASSIGNMENTS—READ INSTRUCTIONS VERY, VERY CAREFULLY!! You have to be very, very careful with ALL the components in myitlab. The software is extremely specific—it IS case- sensitive, and if you add a space where there shouldn’t be (or vice versa), or forget to include a punctuation mark (or vice versa), myitlab will mark it wrong. When you do your assignments, you must read the instructions extremely carefully, not “skimming over” any of the instructions, just in case you miss a tiny requirement. 38

PRINT OUT ASSIGNMENT MARKS Please make sure that as soon as you get your MARK for ANY assignment, that you do the following: DO NOT CLOSE the dialog box with your mark on it--before doing the following: 1. Hit your PRINT SCREEN button on your keyboard 2. Open MS WORD 3. PASTE 4. Enlarge the “screen capture”, so that it’s readable 5. PRINT out your MARK, AND SAVE the file to the DESKTOP -then UPLOAD the file to SkyDrive 6. You may now close the dialog box. There have been some students who have gotten their mark, but when they close the dialog box with the mark on it-- they receive a “0” in their GRADEBOOK. (This is the mark that I see). This “print out” will be your backup copy—put it in a safe place, until the end of the semester. 39

SUBMITTING ASSIGNMENTS: CLICK ON: UPLOAD COMPLETED FILE BROWSE to where your file is > UPLOAD> FINISH: SUBMIT FOR GRADING After submitting assignment, there is a time lapse. You can view results by going to VIEW SUBMISSIONS

Will give 3 files: 1.SUBMITTED FILE 2.SUMMARY REPORT 3.MARKED UP REPORT 1.SUBMITTED FILE Opens a.zip file which is a COPY of the file you submitted for your assignment

SUMMARY REPORT: click on the arrow to EXPAND the information, to find out exactly where you went wrong.

1.MARKED UP REPORT:  Click on the check-mark or x- icons to view the detailed results and score of the corresponding instruction step.  If the project required you to insert images or art, those items are hyperlinked and can be selected for more details.  Missing items are highlighted in tan color.  Hidden elements are highlighted in pale yellow color.  Elements that were to be deleted are highlighted in orange color.

REMOVE SORT HOME tab, in the SORT & FILTER group, click the REMOVE SORT button:

FILTER BY SELECTION in a “TABLE” HOME > SORT & FILTER group > click on the FILTER icon > To FILTER: Click on the drop-down arrow on the COLUMN HEADING (field) you want to filter Select or de-select the VALUES you want to filter

NUMBER FILTERS Click on the drop-down arrow on the COLUMN HEADING (field) you want to filter NUMBER FILTERS > select one of this options: When you select “Less Than” or “Greater Than”, by default it will Also contain “Equal To”, so key in The next number UP (for GREATER than), or The next number DOWN (for LESS than) I.E. If you want >200, you would have to key in >201 (as it contains “equal to”, and will flag “200” also)

FILTER BY FORM SORT & FILTER group ADVANCED button FILTER BY FORM

FILTER BY SELECTION in a “QUERY” To filter all the rows in a table that contain a value that matches a selected value in a row Right-click the VALUE you want to filter. > select: “EQUALS” the specific value you want IF A FILTER IS ALREADY APPLIED: HOME tab, > SORT & FILTER group, > Advanced, > click: CLEAR ALL FILTERS.

ADDING A “TOTAL” ROW IN A QUERY QUERY TOOLS DESIGN tab, > SHOW/HIDE group, click the TOTALS button In the TOTAL row below the AMOUNT field, click the drop-down arrow and select: MIN. DESIGN tab, > RESULTS group, > RUN button. VIEW the query in DESIGN view

HYBRID: MYITLAB MYITLAB HOMEWORK: 2.myitlab TRAINING: Access VOLUME 1- “Skill-Based TRAINING” 1.myitlab ASSIGNMENT: “EXPLORING series” Access Chapter 1- GRADER PROJECT [HOMEWORK]