Lab 21

1. The previous two labs have introduced the concept of a database—a piece of software that stores (maintains) data on a disk drive, and releases this data to a client as requested. This description fits a file system as well except that for the simpler file system the user is expected to know the format of the data on the disk and its organization. All the file system does is bring disk sectors into memory and allow the user to access the sector contents by keeping a file pointer for sequential access and calculating the access point for random access. The file systems relieves the program of the buffer management so that the program can pretend that the whole file is in memory and any record can be accessed with simply a GET # or PUT #. In contrast, the DBMS allows the program to pretend that all the data is organized into tables, and that new tables can be automatically generated via projection or inner join operations. The DBMS accepts commands to generate such tables and returns to the program a set of records that satisfy the command. The program does not have to know about buffering these records, or how they were generated, or how the data actually resides on the disk drive. The transition of data from drive to program is taken care of by the DBMS and the program’s agent the ADO control. The program generates the specification of the recordset, sets this specification in the ADO, and triggers the ADO to interact with the DBMS and refresh the local store of data. Commands can then be issued to manipulate the local data. Once the local data is processed, the ADO is instructed to returned it to the DBMS. The ADO acts as the program’s buffer and other controls can be connected to this buffer to permit the program and the user to give instructions to the ADO concerning its records. These processing controls, like the DataGrid , react to any changes made to the recordset. Indeed, data aware controls can use data from multiple recordsets as illustrated in Figure 18.22 where a value is moved from one control to another and used to update a recordset. The ADO is not the only control that can serve as a pipe from the DBMS to the program, the Data Environment Designer, illustrated in sections 18.10 is an alternative and more powerful control for this task. It also makes a connection to the DBMS and retrieves a recordset, but it has more convenient commands for operating on the records. Both permit the program to send SQL commands through the pipe to be executed by the DBMS. Complete lab 20.

As a review of where we have come, fill in the following table which lists programs that we have studied and/or written, determining the purpose of the illustration and how well you feel you have absorbed the point and feel comfortable with the code:

Program	VB feature(s) illustrated for the first time	% mastered
Ex 5.16	FOR/NEXT	80
Ex 5.21	FOR/NEXT	60
Fig 6.19	INT (X * RND( )), IMGDIE.PICTURE=LOAD, CASE	40
Fig 6.24	ENUM, SUM = , DON’T REALLY REMEMBER USING	0
Ex 6.16	FILLCHARACTER #	40
Ex 6.39	NOT THE FIRST TIME USED	85
Fig 8.13	ISNUMERIC, VAL, STR$	70
EX 8.28	FIRST TIME INTRODUCED, BUT NEVER USED	0
Fig 10.22	LIST BOX	90
Fig 10.41	MSGBOX	80
Fig 11.10	MDI FORMS	85
Fig 11.15	MULTIPLE FORMS	80
Fig 11.16	MAIN, STARTUP	20
Fig 12.3	NOTHING NEW	80
Fig 12.5	FORM_MOUSE DOWN	75
Fig 12.7	SHIFT, ALT, CTRL	65
Fig 12.13	NOTHING NEW	65
Fig 12.14	KEY PREVIEW	70
Fig 13.1	DIVIDEBYZERO, ON ERROR GOTO	40
Fig 13.5	ERR	50
Fig 13.7	RESUME	60
Fig 13.9	STACK ERROR HANDLING	55
Fig 13.10	RETHROWING ERROR	70
Fig 14.9	FILESYSTEMOBJECT	60
Fig 14.17	TEXT STREAM, PATH,	40
Fig 14.19	TRIM$	60
Fig 14.20	EXTRACTING, END OF SREAM	50
Fig 15.4	TYPE, CLOSE, PUT	55
Fig 15.5	.TEXT =“”	60
Fig 15.6	STRING * 15, LENB(UDT)	50
Fig 15.7	GET	60
Fig 18.15	ADODC1	80
Fig 18.20	DATACOMBO DATALIST	80

Program	VB feature(s) illustrated for the first time	% mastered
Ex 5.16	For/Next Loop	85%
Ex 5.21	Nested For/Next Loops	85%
Fig 6.19	Select Case	100%
Fig 6.24	Enum	50%
Ex 6.16	No idea what is new and don’t remember how we did it.	0%
Ex 6.39	No idea what is new and don’t remember how we did it.	0%
Fig 8.13	IsNumeric, Val and Str$	75%
EX 8.28	Mid$, Right$, Left$	85%
Fig 10.22	ListBox	85%
Fig 10.41	Frames and MsgBox	85%
Fig 11.10	MDI	100%
Fig 11.15	Unload and Load	100%
Fig 11.16	Using Main in .bas as startup form	65%
Fig 12.3	MouseEvents	90%
Fig 12.5	Detecting Mouse Buttons	90%
Fig 12.7	Shift	90%
Fig 12.13	Key Events	85%
Fig 12.14	Key Preview	30%
Fig 13.1	Error handler	75%
Fig 13.5	Err object	80%
Fig 13.7	Resume	85%
Fig 13.9	Call stack	50%
Fig 13.10	Rethrowing an error	75%
Fig 14.9	FSO	75%
Fig 14.17	Writing to a Sequential file	85%
Fig 14.19	Reading from a Sequential file	85%
Fig 14.20	Get file and open text stream for reading	75%
Fig 15.4	Creating empty records	85%
Fig 15.5	Writing to a random access file	85%
Fig 15.6	Reading sequentially from Random Access File	80%
Fig 15.7	Random reading of a RAF	80%
Fig 18.15	Querying Database	75%
Fig 18.20	DataCombo and DataList controls	80%

3. Point your web browser at http://cbt.cs.ualr.edu. Log on with the user name <two initials><last name> in caps (no password). Click on the green Training button and then run the unit Introduction to Data Access under Microsoft Visual Basic.

		Microsoft Visual Basic
			Microsoft Visual Basic 6.0 Desktop: Creating COM Components 1
			Microsoft Visual Basic 6.0 Desktop: Introduction to Data Access
			Microsoft Visual Basic 6.0 Desktop:

Summarize below how this material supplements the text presentation. I THINK THAT THE TRAING TURTORIALS SHOULD BE USED IN FILIMILRIZNG. I LIKE IT EVERY MUCH BECAUSE IT SEEMS TO GIVE A CLEAR UNDERSTANDING OF WHATS ACTUALLY BEING PRESTENTED IN THE TEXT.

Each module contains a small tutorial and then exercises to practice your newly learned information. Also, the exercises include questions that are intended to help the user think about the ways that the information can be applied to programming needs.