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Relational databases Week 8 Information Technologies 17:610:550:01 - Fall 2008 -

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Presentation on theme: "Relational databases Week 8 Information Technologies 17:610:550:01 - Fall 2008 -"— Presentation transcript:

1 Relational databases Week 8 Information Technologies 17:610:550:01 - Fall

2 Announcements Quiz grades are in Assignment 3 is due next week MS Access 2007 CDs available

3 Agenda Recap Excel Tables Relational Databases –Basic concepts –MS Access End of class feedback questionaire

4 Last class we covered… … Basic excel capabilities –Automatic calculation using formula/functions –Making sense of data using conditional formatting Charts But there is much more which we will not cover in this class but will give a gist –Working with large amount of data - tables –Making sense of data Sort/Filter Pivot Table

5 Excel Tables First row contains field names Each row is a record

6 Excel Tables A table is an area in the worksheet that contains rows and columns of similar or related information –Can be used as part of a database or organized collection of related information –Worksheet rows represent the records; worksheet columns represent the fields in a record The first row contains the column labels or field names –Identifies data to be entered in the columns Each row in the table contains a record

7 Excel Tables Every cell in the table area, except the field names, contains a specific value for a specific field in a specific record Every record (row) contains the same fields (columns) in the same order as every other record

8 Create Tables Create table from data already in a spreadsheet: –Select the range of cells that contains the data –Click the Insert tab and click Table in the Tables group The Create Table dialog box appears; make appropriate changes –Click OK to complete the table creation and display the contextual Design tab Create table and then add the data: –Select a range of cells on a sheet –Click the Insert tab and click Table in the Tables group The Create Table dialog box appears asking for the range of data for the table –Click OK to display the contextual Design tab

9 Sorting Data Sorting arranges records in a table by the value in field(s) within a table The sort command puts lists in ascending or descending order according to specified keys Keys are the fields on which records are sorted

10 Sorting Data (continued) Sorted by instrumentSorted by class

11 Multiple Level Sorts

12 Filtering and Totaling Data Data refers to a fact or facts about a specific record or sets of records Information is data that has been arranged in some form and viewed as useful

13 Use AutoFilters A quick way to display a subset of data from a table Filtered data displays only the records that meet the criteria you specify To apply a simple AutoFilter to a data table, click the arrow in the column header

14 Using AutoFilters (continued) Filter drop- down list List filtered to display only juniors

15 Agenda Recap Excel Tables Relational Databases –Basic concepts –MS Access End of class feedback questionaire

16 What is a database system? Database: –a large, integrated collection of data Models something about the real world –Entities (e.g., teams, games) –Relationships (e.g., the Red Sox won the World Series) A Database Management System (DBMS) is a software system designed to store, manage, and facilitate access to databases –Todays focus on relational databases

17 Databases Now…

18 And here…

19 Is the WWW a DBMS? Fairly sophisticated search available –Crawler indexes pages on the Web –Keyword-based search for pages But, currently –Data is mostly unstructured and untyped –Cant modify the data –Cant get summaries, complex combinations of data –Few guarantees provided for freshness of data, consistency across data items, fault tolerance, … The picture is changing –New standards, e.g., XML, Semantic Web, etc., can provide richer models of data

20 Database Basics What is a database? –Collection of data, organized to support access –Models some aspects of reality Components of a relational database: –Field = an atomic unit of data –Record = a collection of related fields –Table = a collection of related records Each record is one row in the table Each field is one column in the table –Database = a collection of tables –Primary Key = the field that uniquely identifies a record

21 A Simple Example NameDOBSSN John Doe04/15/ Jane Smith08/31/ Mary Adams11/05/ Field Field Name Record Primary Key Table

22 Why Relational? Databases model some aspects of reality A relational database is a database that groups data using common attributes found in the data set –The resulting "clumps" of organized data is much easier for people to understand –The grouping uses the relational model MS Access is a relational database management system, or RDBMS

23 Relational Database Terminology Relational DB terminologyMS Access relation, base relvartable derived relvarquery tupleraw/record attributecolumn/field A relation is defined as a set of tuples that have the same attributes. A relation is usually described as a table, which is organized into rows and columns. All the data referenced by an attribute are in the same domain and conform to the same constraints.

24 The Registrar Example What do we need to know (i.e., model)? –Something about the students (e.g., first name, last name, , department) –Something about the courses (e.g., course ID, description, enrolled students, grades) –Which students are in which courses

25 A First Try Put everything in a big table… Discussion: Why is this a bad idea?

26 Goals of Normalization Remove duplicates/Save space –Save each fact only once More rapid updates –Every fact only needs to be updated once More rapid search –Finding something once is good enough Avoid inconsistency –Changing data once changes it everywhere

27 Another Try... Student Table Department TableCourse Table Enrollment Table

28 Approaches to Normalization For simple problems (like the homework): –Start with binary relationships: pairs of fields that are related –Group together wherever possible –Add keys where necessary For more complicated problems: –Entity relationship modeling

29 Some Lingo Primary Key uniquely identifies a record –e.g., student ID in the student table Foreign Key is primary key in the other table –It need not be unique in this table

30 The Data Model Student Table Department TableCourse Table Enrollment Table Primary key Foreign key

31 Relational operations: Join Joined Table Student Table Department Table

32 Relational Operations: Project SELECT Student ID, Department

33 Relational operations: Restrict WHERE Department ID = HIST

34 Relational Operations Joining tables: JOIN Choosing columns: SELECT –Based on their label Choosing rows: WHERE –Based on their contents These can be specified together department ID = HIST SELECT Student ID, Dept WHERE Dept = History

35 Querying a Database Queries allow us to ask a question about data and receive an answer back by returning a subset of the table data. Querying a database will make use of all or part of these relational operations mentioned previously (JOIN,SELECT,RESTRICT)

36 Database Integrity Registrar database must be internally consistent –All enrolled students must have an entry in the student table –All courses must have a name –… What happens: –When a student withdraws from the university? –When a course is taken off the books?

37 Integrity Constraints Conditions that must be true of the database at any time –Specified when the database is designed –Checked when the database is modified RDBMS ensures that integrity constraints are always kept –So that database contents remain faithful to the real world –Helps avoid data entry errors

38 Discussion Point How is a relational database different from a spreadsheet?

39 Spreadsheet or Relational DB? You are working with large amounts of data You need to create relationships between your data You rely on external databases to analyze data Your data is of a manageable data size There is no need for relationships between data You are primarily creating calculations and statistics Use Relational DB when: Use spreasheets when:

40 Agenda Recap Excel Tables Relational Databases –Basic concepts –MS Access End of class feedback questionaire

41 MS Access Intro to MS access Relational Databases and Multi-table queries

42 Open a Database Open Recent Documents list Choose Open to browse for a file or choose a database from the Recent Documents list

43 Open a Database Open Recent Database list Open a New database Open from a Template When you first open MS Access this is the first screen you see.

44 MS Access Database Terminology Field Record Table Database A database is made up of one or more tables Individual tables in a database Records Individual fields

45 Objects Tables Queries Reports Forms Macros Modules Objects

46 Work with Table Views Datasheet View – used to add, modify, delete and view records Design View – used to create and modify the fields in a table Design View Datasheet View

47 Work with Table Views Click the Home tab Click View from the View ribbon Table View Options

48 Datasheet View Primary Key – a field that identifies each record as being unique Primary Key

49 Design View Click F6 to switch between the upper and lower panes Key symbol identifies primary key field Set field properties in the lower pane

50 Backing-up and Renaming Access Files Save As – different in Access than other Office applications –Save As saves only the current object, not the entire database To save a database with a new name you must either: –Backup the database –Copy, paste, and rename the database

51 Backing-up a Database Backing-up an Access file will produce a copy of your file with a default filename Default filename of a backup file is the name of the database and the current date

52 Compact and Repair Compact and Repair is located under the Manage menu Fixes problems due to inefficient file storage and growth of a database –Should be performed everyday –Often decreases the file size by 50% or more

53 Filters Create a subset of records Do not change underlying table data Two types –Filter by Selection –Filter by Form

54 Filter by Selection Selects only the records that match pre-selected criteria Table before filter by selection Results of filter Filter by selection being applied from pre- determined criteria

55 Applying and Removing a Filter Once a filter is applied, the Toggle Filter icon will be available The Toggle Filter icon can be used to apply and remove the current filter as many times as desired Filter icon in the Sort and Filter group Toggle Filter icon

56 Sorting Table Data Lists records in ascending or design order according to one or more fields Last Name field sorted ascending Last Name field sorted descending

57 Recap: Excel or Access? You are working with large amounts of data You need to create relationships between your data You rely on external databases to analyze data Your data is of a manageable data size There is no need for relationships between data You are primarily creating calculations and statistics Use Access when:Use Excel when:

58 Recap: Relational Database-RDBMS Relational database management systems allow data to be grouped based on common attributes. Data is grouped into tables and relationships are created between the tables This is much more efficient than the opposite of an RDBMS which is a flat file. Flat files store data in one single file with no special groupings or collections

59 MS Access Intro to MS access Relational Databases and Multi-table queries –Tables/Database Design Consideration –Creating Tables –Creating relationships between tables –Querying the Database

60 Table Design Considerations Just as you first create a blueprint to build a house, you should first sketch or outline the design of a database table Careful pre-planning will save you much time in the future All design decision are done when you are in the Design View of the Table

61 Design Considerations – Field Size Property Set the field size in Table Design View Always anticipate the current field size may one day need to be larger Set field size in the Field Properties grid of Table Design View

62 Design Considerations – Validation Rules Used to avoid data entry errors by restricting what can be entered Validation text can be used to provide an explanation of the type of data that is allowed in a field Eg: <>0 will not allow 0 to be a value of the field Set validation rules in the Field Properties grid of Table Design View

63 Design Considerations - Indexing Indexing helps sorting and search process Can be set to disallow duplicates (which sometimes in needed) – example when is needed? Relates the field values to the records that contain the field value Indexed Property

64 Design Considerations – Store Data in its Smallest part For greater flexibility, store data in its smallest part –Instead of one field for an address, use many –Instead of one field for a name, two or three Like this Not like this

65 Design Consideration - Plan for Date Arithmetic Using a data type of date/time for all date fields allows the use of date arithmetic Fields declared as a data type of Date/Time

66 Design Considerations – Design Multiple Tables Using multiple tables helps reduce redundancy –The process is also referred to as normalization Multiple table tabs identify open tables Multiple tables shown in the Navigation pane

67 MS Access Intro to MS access Relational Databases and Multi-table queries –Tables/Database Design Consideration –Creating Tables –Creating relationships between tables –Querying the Database

68 Creating Tables – From the Create Tab Enter data directly into a table, including the field names Enter field names, data types and descriptions in Table Design View Begin with a template When you create a new table is good practice to start with the Table Design to enter field names, data types, properties

69 Creating Tables – From the Import Tab Click the application from which to import or Choose the type of file you wish to import Click the appropriate application button Choose a file type to import

70 Recap: Work with Table Views Click the Home tab Click View from the View ribbon Table View Options

71 Recap: Table Design View Key symbol identifies primary key field Set field properties in the lower pane

72 Create Tables – Specifying field names After choosing your method of creation begin implementing the table design –Use CamelCase notation for field names (e.g., LastName, i.e, no spaces) –Specify data types –Establish a primary key –Consider the need for a foreign key Table Table Design View Add field in Table View

73 Create Tables – Primary Key Tables are automatically created with an AutoNumber field which serves as the primary key To change the primary key –Select a field in Table Design View –Click the primary key icon Primary Key Field Primary Key icon

74 Create tables - Field Properties Field Properties can be used to specify characteristics for individual fields Located in the lower pane of Table Design View Field Size property Indexing

75 Recap: Datasheet View Here you enter values in your table after you designed your table in the Table Design View Primary Key – a field that identifies each record as being unique Primary Key

76 MS Access Intro to MS access Relational Databases and Multi-table queries –Tables/Database Design Consideration –Creating Tables –Creating relationships between tables –Querying the Database

77 Tables Relationships The strength of Access is the fact that it is a relational database –This means you can have multiple tables and create relationships between each table –This helps eliminate redundant data Relationship between two tables Primary key Foreign key

78 Foreign Key Customer ID - Primary Key in Customer Table Customer ID –will only appear in one record - there must only be one unique id per customer Customer ID - Regular Field in Orders Table Customer ID may appear many times – one customer can place many orders Foreign key is used to establish relationships between tables Based on the above example: –Customer Id is the foreign key in the Orders table –This is referred to as a One to Many Relationship

79 Establishing Relationships - Using the Relationship Window Click the Database tools and click the Relationships icon First time of access will be empty and you need to add tables Add the tables or queries from the Show table dialog box Relationships icon Show Table dialog box Relationship window

80 Establishing Relationships In the Relationship window, click and drag a field name from one table to a field name in a related table Click and drag to create a relationship

81 Establishing Relationships Enter the appropriate settings in the Edit relationships dialog box and click Create A join line will appear when one table is joined to another Infinity symbol notes referential integrity has been applied Set referential integrity and cascades

82 Referential Integrity Assures that the references to relationships between data is accurate Established when creating the relationship between two tables Enforce Referential Integrity

83 Cascades When active, data changed in one table that is in a relationship will be changed in its related tables Can be set when establishing relationships between tables Cascade update and cascade delete

84 MS Access Intro to MS access Relational Databases and Multi-table queries –Tables/Database Design Consideration –Creating Tables –Creating relationships between tables –Querying the Database

85 Queries Queries allow us to ask questions about data This record set that answers our question is called a dataset Employees table Dataset resulting from querying table for only employees who are Sales Representatives

86 Create Queries - Using Query Design View From the Create Tab select Query Design from Other group Two panes – the table pane and the design pane Striking the F6 key will toggle you between sections Tables pane Design pane Create Tab

87 Select Query Searches associated tables and returns a dataset that matches the query parameters Changes made to the dataset will be reflected in the associated tables

88 Specifying Criteria in a Select Query Field row – displays the field name Sort row – enables you to sort the dataset Show row – controls whether or not you see a field in the dataset Criteria row – determines the records that will be selected for display Fields in design grid allow us to specify criteria for the dataset

89 Specifying Criteria – Currency and Operands Specify criteria with currency –Without the dollar sign –With or without the decimal point Use operands such as: – Less than and greater than – Equal to or not equal to Greater than (>) operand Currency amount entered without dollar sign

90 Specifying Criteria – Wildcards Asterisk - searches for a pattern that includes any number of characters in the position of the asterisk Question mark - searches for a pattern that includes a single character in the position of the question mark Query with asterisk wildcard and resulting dataset Query with question mark and asterisk wildcard and resulting dataset to specify criteria for the dataset

91 Specifying Criteria – Null Values IS NULL finds only records that have no value IS NOT NULL excludes Null value records Is Null criteria and resulting dataset IS NOT NULL criteria and partial resulting dataset

92 Specifying Criteria – And and Or OR finds records that can match one or more conditions AND finds records that must match all criteria specified Or Criterion and resulting dataset And criterion and resulting dataset

93 Copy a Query Sometime we might want to do several queries that different only by one or two attributes Right click on the query - chose Copy form the shortcut menu Right click and chose paste In the Paste as dialog box, give the query a new name

94 Run a Query Running, or executing, a query is done by clicking the Run command Run command

95 Creating Queries – Using the Query Wizard From the Create tab, choose Query Wizard for the Other group Choose query type from the New Query dialog box Select Simple Query Wizard Query Wizard icon

96 Creating Queries – Using the Query Wizard: continued Select the Table/Queries to include and choose the desired fields Select aggregate totals needed in the Summary Options box

97 Creating Queries – Using the Query Wizard: continued Title your query and open in Datasheet View or Query Design View

98 Sharing Data with Excel Data can be imported from Excel –It may be appended to an existing table –It may be used to create a new table Excel icon External Data tab

99 Sharing Data with Excel Select the Excel file you would like to import Select how you would like to import the data –Appended – added to the end of an existing table –New table – creates a new table in a database –Linked – create a new table that is linked to the source file in Excel Select the Source Select the destination


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