1. Database Beginnings CIS 121 – Computer Concepts II Instructor: Ron Christensen

2. 11/18/2015CIS 121 - Portland Community College 2 What is Data? Data are facts about things, places, events Facts about data are called metadata Data are building blocks for information

3. 11/18/2015CIS 121 - Portland Community College 3 Common Data Applications Word Processors – Like fifth generation language, very difficult to track Spreadsheets – Mostly two dimensional. When items change, multiple spreadsheets become problem some. Databases – More efficient, real-time, on- line.

4. 11/18/2015CIS 121 - Portland Community College 4 DBMS – Database Management System DBMS software… –Manages metadata –Organizes data –Enforces security –Manages access to data and metadata –Enforces integrity

5. 11/18/2015CIS 121 - Portland Community College 5 Database Information System Figure 1.2 InputOutput

6. 11/18/2015CIS 121 - Portland Community College 6 What is a Database (Black Box)? A computer accepts input, processes it according to some rules, and makes output. Everything will be represented as data, including the input and the output So what the DBMS is doing is taking the data produced (the input) and converting it into information (the output)

7. 11/18/2015CIS 121 - Portland Community College 7 Relational DBMS Relational refers to the method of organizing data, i.e. in tables Developed in the1970s Most common of several different types of DBMS systems –Hierarchical –Network –Object

8. 11/18/2015CIS 121 - Portland Community College 8 Microsoft ACCESS Relational DBMS software for Windows Available as part of MS-Office

9. 11/18/2015CIS 121 - Portland Community College 9 Type of Databases Production Database –Transaction oriented –Lots of well-defined read/write/update actions Decision Support Database –Query oriented –Complex queries –Few updates or writes

10. 11/18/2015CIS 121 - Portland Community College 10 A Bigger Picture… Databases are a critical part of information systems Information systems help people solve problems Your personal database and web page will form the basis of a personal information system

11. 11/18/2015CIS 121 - Portland Community College 11 Database DBMS Operating System Software Hardware People Application Programs Write and Use Design and Manage Information System Figure 1.2

12. 11/18/2015CIS 121 - Portland Community College 12 Entities Entities are anything about which you want to know something –People, places, things, events, concepts Data are facts about entities

13. 11/18/2015CIS 121 - Portland Community College 13 Entity Sets Entity sets are collections of related entities. Entities are related by their classification: student entities are related by the fact that they are all students invoice entities are related by the fact that they are all invoices car entities are related by the fact that they are all cars

14. 11/18/2015CIS 121 - Portland Community College 14 Entity Sets, cont. Entity sets are named as a broad definition of the whole entity. Entity and Entity set names are singular. Entity and Entity set names are capitalized. Examples: An entity named HR contains HR entities. An entity named EMPLOYEE contains employee records. An entity named DEPARTMENT contains department records.

15. 11/18/2015CIS 121 - Portland Community College 15 Entity Sets, cont. Entity Sets can only contain related records –a STUDENT entity set may not contain INVOICE data –a DEPARTMENT entity set may not contain invoice data –a PRODUCT entity set may not contain employee data …. And so on

16. 11/18/2015CIS 121 - Portland Community College 16 Relational Databases Data is stored in TABLES (also called relational sets) Tables are collections of attributes for related records The reality is that lots of different things get stuffed into a table for a variety of reasons (Tables are another word for entity sets)

17. 11/18/2015CIS 121 - Portland Community College 17 Database Tables A database table is used to store a record (or tuple) –An entity set is a collection of related records An record is anything you want to keep track of, so an entity may be a person, place, thing, event, etc. –(Record is another word for Entity)

18. 11/18/2015CIS 121 - Portland Community College 18 Database Table Components At the conceptual level, a database table may be viewed as a matrix. –Matrix rows are also known as tuples or records each row contains an record –Matrix columns are also called fields or attributes. Each column (field) contains the record’s attribute values

19. 11/18/2015CIS 121 - Portland Community College 19 Attributes Attributes are the characteristics that describe records –A STUDENT record may be described by attributes that may include... social security number name address date of birth major

20. 11/18/2015CIS 121 - Portland Community College 20 Records, Attributes, Data Records are things about which you want to know something, e.g. STUDENT Attributes describe something about the entity, e.g. the name of the student Data are the values of the attributes, e.g. DOE, JOHN

21. 11/18/2015CIS 121 - Portland Community College 21 Null A null is an absence of value A null is NOT –A blank –A zero A null has several meanings in a database –Value does not exist –Value is not known

22. 11/18/2015CIS 121 - Portland Community College 22 Attribute Names Attribute names are capitalized. For documentation reasons, attribute names are composed of two parts: –the first few characters reflect the entity they help describe. –subsequent characters are sufficiently descriptive to identify the attribute.

23. 11/18/2015CIS 121 - Portland Community College 23 Attribute Names, cont. Examples of attribute names: EMP_LNAME = employee last name STU_GPA = student grade point average PROD_CODE = product code CUST_LNAME = customer last name INV_NUM = invoice number

24. 11/18/2015CIS 121 - Portland Community College 24 Keys Primary Key (PK) –an attribute (or combination of attributes) that uniquely identifies each row (tuple) in a table. A PK composed of two or more attributes is known as a composite PK. Foreign Key (FK) –an attribute in one table whose values match the PK values in a related table or whose “values” are null. FKs are used to link (connect) related tables.

25. 11/18/2015CIS 121 - Portland Community College 25 Data Integrity. Entity Integrity –PK uniquely identifies each entity in a table PK may not include nulls Referential Integrity –FK values in one table match the PK values in the related table FK may not include nulls

26. 11/18/2015CIS 121 - Portland Community College 26 A Conceptual View of a Database Table Named attributes (fields) The Primary Key (PK) is a unique record identifier. If you know the PK value, you will know all of its row’s attribute values Each row represents an record A row is also called a tuple. Each row/column intersection contains only one of an entity’s attribute values Each column contains the values of an attribute. The EMP_FNAME column only contains employee first names; the EMP_PHONE may only contain employee phone numbers. Tables are named. The table you see here is the EMPLOYEE table.

27. 11/18/2015CIS 121 - Portland Community College 27 Entity Integrity A table exhibits entity integrity when all of its Primary Key (PK) values uniquely identify each table row (record.) EMPLOYEE table 1. A PK cannot contain duplicate values 2. A PK cannot contains nulls Note: A null indicates the absence of a value; it is not a blank. (You create a null when you tap the ENTER key without first making an entry. A blank is created when you tap the space bar and then tap the ENTER key.)

28. 11/18/2015CIS 121 - Portland Community College 28 Foreign keys (FK) and Referential Integrity To maintain referential integrity, a foreign key (FK) must reference an existing PK value in a related table it may be null. A Foreign Key (FK) is an attribute located in one table that “points to” a Primary Key (PK) in a related table. The use of FKs allows you relate one table to another. INVOICE table LINE table

29. 11/18/2015CIS 121 - Portland Community College 29 1.Simple (atomic) 2.Composite A.Single-valued B.Multi-valued Derived Attribute types

30. 11/18/2015CIS 121 - Portland Community College 30 Simple (Atomic) Attributes A simple (atomic) attribute cannot be decomposed into meaningful components Examples: –The attribute EMP_LNAME cannot be decomposed, because you cannot subdivide EMP_LNAME into a set of new attributes. –The attribute PROD_PRICE cannot be decomposed, because you cannot subdivide PROD_PRICE into a new set of attributes.

31. 11/18/2015CIS 121 - Portland Community College 31 Simple (Atomic) Attributes, cont. Simple attributes may be …. single-valued or multi-valued

32. 11/18/2015CIS 121 - Portland Community College 32 Simple (Atomic) Attributes, cont. Single-valued simple attributes Example: an employee can have only one gender, so EMP_GENDER is a single-valued attribute. The attribute EMP_GENDER cannot be decomposed, so it is a simple attribute. Multi-valued simple attributes Example: an employee can have many degrees, so EMP_DEGREE is multi-valued. The attribute EMP_DEGREE cannot be decomposed, so it is a simple attribute.

33. 11/18/2015CIS 121 - Portland Community College 33 Composite Attributes A composite attribute can be decomposed into meaningful components Example: an employee’s address, shown as 123 East Main Street, Nashville, TN 32123 may be decomposed into EMP_ADDRESS = 123 East Main Street EMP_CITY = Nashville EMP_STATE = TN EMP_ZIP = 32123

34. 11/18/2015CIS 121 - Portland Community College 34 Composite Attributes, cont. A composite attribute may be …. single-valued or multi-valued

35. 11/18/2015CIS 121 - Portland Community College 35 Composite Attributes, cont. single-valued composite attributes –Example: an employee can have only one date of birth, so EMP_DOB is single-valued. But the attribute EMP_DOB can be decomposed into year, month, and day, so it is a composite attribute. multi-valued composite attributes –Example: an employee can have more than one address, so EMP_ADDRESS may be multi-valued. The attribute EMP_ADDRESS can be decomposed into street address, city, state, and ZIP code, so it is a composite attribute.

36. 11/18/2015CIS 121 - Portland Community College 36 Attribute Storage Each table row/column intersection contains a single attribute value for a single entity. –Ideally, attributes are simple and single-valued. –Single-valued composite attributes are acceptable but composite attributes may make queries more complex and may impose reporting limitations. –Multi-valued attributes, either simple or composite, may create structural problems make queries more complex and may impose reporting limitations. May be necessary for a variety of reasons, but should be avoided where possible

37. 11/18/2015CIS 121 - Portland Community College 37 Multi-valued Attribute Storage Multi-valued attributes are sometimes stored as –strings this approach yields query complexity and reporting limitations –multiple attributes this approach yields structural problems Ideally, multi-valued attributes are handled through the use of composite tables.

38. 11/18/2015CIS 121 - Portland Community College 38 Multi-valued Attributes Stored As Strings Multi-valued attribute Poor practice: Makes it difficult to generate queries such as “How many employees have earned BA or MBA degrees?”

39. 11/18/2015CIS 121 - Portland Community College 39 Storing Multi-valued Attributes In Separate Columns Poor structure: many nulls table structure must be altered when additional degrees are earned

40. 11/18/2015CIS 121 - Portland Community College 40 Composite Tables Multi-valued attributes can generate many nulls, increasing uncertainty about the data One solution is to add another table, called a composite table or bridge table It is often better to use more tables rather than poor attributes in fewer tables

41. 11/18/2015CIS 121 - Portland Community College 41 Table name: DEGREE Table name: EMPLOYEE Table name: EDUCATION A Composite Table (EDUCATION) is Used To Convert M:N Relationships To 1:M Relationships

42. 11/18/2015CIS 121 - Portland Community College 42 Supertype/Subtype Relationships Are Used To Eliminate or Control the Occurrence of Nulls A table with many nulls Subtype. (Table name: PILOT) Supertype. (Table name: EMPLOYEE

43. 11/18/2015CIS 121 - Portland Community College 43 Relationships Tables can be related to each other in a variety of ways –1:1 Relationships –1:M Relationships –M:N Relationships –Recursive Relationships Tables are related by their PKs and FKs

44. 11/18/2015CIS 121 - Portland Community College 44 1:1 Relationships Entity in one table is related to only one entity in another table Example –STUDENT : SOCIAL SECURITY NUMBER Each student has only one Social Security Number, each Social Security Number refers to only one student

45. 11/18/2015CIS 121 - Portland Community College 45 1:M Relationships Entity in one table is related to many entities in another table Example –STUDENT : TUITION INVOICE Each student may have several tuition invoices, each tuition invoice is assigned to only one student

46. 11/18/2015CIS 121 - Portland Community College 46 M:N Relationships An entity can occur more than once on both sides of the relationship – causes several different problems in databases Example: –STUDENT : CLASS Each student may register for many classes, each class may contain many students

47. 11/18/2015CIS 121 - Portland Community College 47 Some Issues with M:N May signal redundant data, resulting in anomalies –Modification anomaly –Deletion anomaly Keep it simple: DO NOT IMPLEMENT M:N RELATIONSHIPS. Use composite tables instead

48. 11/18/2015CIS 121 - Portland Community College 48 Recursive Relationships Entity is related to itself Examples –TEAM : TEAM Teams in an athletic league play each other –CLASS : CLASS Some classes are pre-requisites for others

49. 11/18/2015CIS 121 - Portland Community College 49 Optional (vs. Mandatory) Relationships Optional relationships occur when entities in two tables may be related, but do not need to be. Example (Optional Relationship): –STUDENT : SOCIAL SECURITY NUMBER A student is not required to have a social security number Example (Mandatory Relationship) –STUDENT : CLASS A student must be registered in a class to be a student

50. 11/18/2015CIS 121 - Portland Community College 50 End of Lecture