BIT 5474

Data
(DBMS)
Messaging
Knowledge
(KBMS)
Models
(MBMS)
Dialog
(GUI)
User
Source: Turban, E and Jay E. Aronson, Decision Support Systems and Intelligent
Systems, 5th Ed.
, Prentice Hall, 1998.

Databases
Where are we?
Automated Data
Acquisition using VBA
The Web
Data Models
Decision Modeling with Excel
3

Excel Data Retrieval
We can retrieve data to Excel from a number of different external sources:
4

 To import a webpage, there are a few new properties needed.
With ActiveSheet.QueryTables.Add(Connection:= _
"URL;http://www.nvc.vt.edu/rmajor/bit5474/schedule.htm", Destination:=Range( _
"$A$1"))
.CommandType = 0
.Name = "schedule"
.FieldNames = True
.RowNumbers = False
.FillAdjacentFormulas = False
.PreserveFormatting = True
.RefreshOnFileOpen = False
.BackgroundQuery = True
.RefreshStyle = xlInsertDeleteCells
.SavePassword = False
.SaveData = True
.AdjustColumnWidth = True
.RefreshPeriod = 0
.WebSelectionType = xlAllTables
.WebFormatting = xlWebFormattingNone
.WebPreFormattedTextToColumns = True
.WebConsecutiveDelimitersAsOne = True
.WebSingleBlockTextImport = False
.WebDisableDateRecognition = False
.WebDisableRedirections = False
.Refresh BackgroundQuery:=False
End With
5

 An example webpage imported to Excel using VBA
6

Access Data Retrieval
We can retrieve data from a database using the following techniques:
• QueryTables
• ADO, RecordSets (rs), and SQL statements
7

Getting Data into Excel 2013 from Access 2013 using
QueryTables
Excel will let you choose which saved Queries (or VIEWS ) you want to execute, or which Tables you want to retrieve data from.
Drag the bottom left corner of the window to enlarge it.
8

Getting Data into Excel 2013 from Access 2013 using
QueryTables
Next, tell Excel where you want to put the query results.
9

Getting Data into Excel 2013 from Access 2013 using
Active Data Objects (ADO)
The second method we will use for retrieving data uses ADO .
Before using ADO, you need to activate the relevant components in VBA.
Go to Tools | References in VBA, then scroll down the list of available references and select the Data references shown below.
10

 ActiveX Data Objects

It is a “go-between” – an interface
For us, it is an interface between Excel and
Access
Excel
Access

 With ADO, we can write relatively simple code in VBA to retrieve data from an external database
 ADO has an object model – we will just use that
 See object browser
– Before and after

Excel rs results rs cn
Access

 In general, you can:
 add a record to the set
 edit a record in the set
 delete a record in the set
– Then put the whole new Recordset back into the database
 You can also :
 put results in a Worksheet
 populate a ComboBox
 Work with the numbers in the Recordset

Etc… 14

 A recordset is a “set of records.”
– It resides temporarily in memory and
– not on a hard drive
 The recordset contains either
– the result of a query, or
– an entire database table

 Databases are persistent :
– They continue to exist once you have quit your program
 Recordsets are not persistent :
– They will go away (forever) once you end your program, close the database, etc.
16

Open ing
 We must specify 2 items before we can
Open a recordset:
– The SQL statement that tells what to
“grab” out of the database, and
– The Connection object that tells the kind of database we have and where it is (see above)
For example: rs.Open SQL, cn

 Step 1. Create a new instance of the recordset object:
Dim rs as new ADODB.Recordset
 Step 2: Develop a connection string strConnect = "Provider=Microsoft.ACE.OLEDB.12.0;
Data Source=" & Path & "HokieStore.accdb;"

 Step 3: Configuring the Cursor Properties
 A cursor is used to:
– control record navigation
– control the visibility of changes in the database
– control the updatability of data
 We assign values to the following three properties:
1. CursorLocation
2. CursorType
3. LockType

 Step 3.1: Determine the best cursor location
– The CursorLocation property sets or returns a long value that indicates the location of the cursor service.
 adUseServer (default)
 adUseClient
– Uses a client-side cursor supplied by a local cursor library.
– Use this option for our class rs.CursorLocation = adUseClient

 Step 3.2: Determine the best cursor type
– The CursorType property sets or returns the cursor type to use when opening a Recordset object.
 adOpenForwardOnly (default)
 adOpenStatic
– Allows us to move back and forward through the recordset.
– Use this option for our class

 Step 3.3: Determine the best lock type
– The LockType property sets or returns a value that specifies the type of locking when editing a record in a
Recordset.
 adLockReadOnly (default)
 adLockPessimistic
– Allows us to change values
– Use this option for our class

 Step 4. Create the query string: strSQL = "Select * FROM Customers"
 Step 5: Develop a connection and populate the recordset (use the open method) rs.Open strSQL, strConnect, adOpenStatic, adLockPessimistic

 Step 6. Leverage the Recordset Object
– Properties
 RecordCount, EOF, BOF, CursorType, etc.
– Methods
 MoveFirst, MoveNext, MoveLast,
MovePrevious

 Step 7. Close Connections rs.Close
 Step 8: Free up system resources
Set rs = Nothing


Once a recordset is “opened,” it is easy to go through its records with a Do loop such as the following:
With rs
Do Until rs .EOF
Statements
.MoveNext
Loop
End with

Database and SQL Background
27

 Purposes of Databases
– Store data efficiently
– Allow users to request data they want, in a suitable form
– Create Information!!!
 Two main types
– Desktop (e.g., Microsoft Access)
– RDBMS – server based (e.g., Microsoft SQL
Server; Oracle)

A ‘Flat File’ Database
RecNo Name
1 John Smith
Address City State Zip Product Units Amount
221 Main St. New York NY 08842 Television 1 500
2 William Chin 43 1st Ave.
Redmond WA 98332 Refrigerator 1
3 William Chin 43 1st Ave.
Redmond WA 98332 Toaster 1
800
80
4 Marta Dieci
5 Marta Dieci
6 Marta Dieci
2 West Ave.
Reno
2 West Ave.
Reno
2 West Ave.
Reno
NV 92342 Television
NV 92342 Radio
NV 92342 Stereo
1
1
1
500
40
200
7 Peter Melinkoff 53 NE Rodeo Miami FL 18332 Computer
8 Martin Sengali 1234 5th St.
Boston FL 03423 Television
9 Martin Sengali 1234 5th St.
Boston FL 03423 Stereo
10 Martin Sengali 1234 5th St.
Boston FL 03423 Radio
11 Martin Sengali 1234 5th St.
Boston FL 03423 Refrigerator 1
1
1
1 1500
1 500
200
40
80

Customers Table:
CusNo Name
1 John Smith
2 William Chin
A ‘Relational’ Database
Address City State
221 Main St.
New York NY
43 1st Ave.
Redmond WA
Zip
08842
98332
Orders Table:
CusNo Product Units Amount
1 Television 1 500
2 Refrigerator 1 800
2 Toaster 1 80
3 Television 1 500
3 Radio 1 40
3 Stereo 1 200
4 Computer 1 1500
5 Television 1 500
5 Stereo 1 200
5 Radio 1 40
5 Refrigerator 1 80






Redundancy (i.e. data duplication)
Multiple value problems
– We could have Order1, Order2,…
– Or, we could have multiple orders in a cell
Update anomalies
– Updating a single customer’s phone number requires you to update multiple entries
Insertion anomalies
– You cannot insert information about an customer until we have acquired the customer data
Deletion anomalies
– If there is a single order for a particular customer, and for some reason we decide to remove the record about the customer, we lose information about the order too

One solution – the Relational Database
Management (RDBMS) model
 Data in the form of tables
 Idea introduced in 1970 by E. F. Codd
 Based on mathematical foundations of relational algebra and calculus
 Commercial databases began to appear around 1980

 A widely used language for creating, manipulating, analyzing and searching through databases.

We’ll just stratch the surface.

SELECT fieldlist FROM recordsource
WHERE searchcondition ORDER BY sortorder

DELETE FROM tablename WHERE condition;

UPDATE tablename SET fieldname = newvalue
WHERE condition;

INSERT INTO tablename (fieldlist) VALUES (valuelist);

CREATE TABLE tablename (field1 type (size),
field2 type (size) [NOT NULL], … );

ALTER TABLE tablename ADD COLUMN fieldname type (size); or
ALTER TABLE tablename Drop COLUMN fieldname;

.AddNew
.AbsolutePosition
.BOF
.EOF
.Delete
.Edit
.Fields
.MoveFirst
.MoveLast
.MoveNext
.MovePrevious
.FindFirst criteria
.FindLast criteria
.FindPrevious criteria
.FindNext criteria
.NoMatch
.RecordCount
.Update