Archive for the ‘dbms packages’ Category

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DBMS packages-4

April 13, 2009

Today we continue our discussion on DBMS Packages. Software packages called Data Base Management System (DBMS) has been developed long before micro-computers to handle the problems of maintaining and integrating large volumes of data on large machines. The most important distinguishing feature of a DBMS package on personal computers is that it provides a very high level language interface which can be learned by a user who is not a computer programmer. We have already talked some important command in our previous post. Today we will talk on other command like quit, use custlist etc….

 

..QUIT

Next day when we start the dBASE III programme, we must first indicate which file we want to use, otherwise dBASE III will not know which file we are interested in. The command for this is

 

..USE CUSTLIST

Now let us say we want to query on the customer data for extracting different types of information. Here is a sample list to illustrate how easy it is. 
 

One has to learn only few additional features to see how sales and receipt transactions can be used to update amount due for each customer. The dBASE III package also has REPORT command for producing user specified reports. With the command verbs, dBASE III also provides conventional programming features like IF-THEN-ELSE, WHILE-DO. A complete set of dBASE III programmes can be designed to implement a medium sized application in a couple of weeks.

 

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DBMS packages-3

January 22, 2009

Note that with this command will have only specified the structure of the record for a file which is to contain customer data. Therefore we should have some way of loading the customer records in the CUSTLIST file. For this purpose we will have to type the following command:

 

..APPEND

With this command we get a screen which provides a blank customer record. As the name implies, this command will append a record to our CUSTLIST file. Thus, it can be used whenever we want to add one more customer to customer list. With the customer we can add product fulfillment types. Product given to customer gives them product fulfillment or order fulfillment. We can add any criteria for that.

 

In the screen provided with above command, we now type the necessary details of a customer. The names of the fields are displayed on the screen to facilitate entry of data for a customer for which we wish to create a record in CUSTLIST file. After we type in all the required details about the customer and type e get another blank record in which we can enter data about next customer and so on. When we type right at the beginning of blank record we get back to dot prompt where we can issue a new dBASE III command.

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DBMS packages-2

January 22, 2009

When we start the dBASE III programme, it prompts by dot (.). Also when it finishes executing a given command, it writes dot in the first column of next line on the screen. Interaction with dBASE III package consists mainly of issuing appropriate commands against this dot prompt. Each dBASE III command starts with a key word (or verb) followed by certain parameters. The command for creating a file for customer data would be

 

..CREATE CUSTLIST

Note the keyword CREATE which is typed by the user against the dot prompt produce by dBASE III. CREATE command wants a parameter which will be used as a name for the file so created. The user can choose any name that he desires within the syntactic rules specified by the package. We shall henceforth omit such minor syntactic details of the package. We shall use the symbol to indicate enter or return key of the keyboard. In response to CERATE command, dBASE III will provide a screen where we can enter the above nine filed names alongwith their type characteristics.

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DBMS packages-1

January 20, 2009

Each record will have to contain details about a customer. What constitutes ‘the necessary details’ will depend mostly on what use we want to make to this data-base. When we create a customer file through dBASE III package, it will first want us to specify the record structure for the file. For a blinds company who are selling vertical blinds, roman shades products online. When they are creating their DBMS file, their criteria is different than for the company who are providing instant life insurance rates and life insurance quotes online.

 

For a customer file we want each record to have nine fields: one each for the items listed above. In dBASE III, it is necessary to give names to each of these nine fields so that they can be later referred to using these names. The field names which we have chosen are shown in the third column above. Apart from the name, we have to also indicate what type of data will be stored in the field and in certain cases number of characters to be reserved to hold the data for that field. We will want AMOUNTDUE and CRDLMT to hold numeric data and all other fields to hold text or character data. Now let us have a quick look at a dialogue in dBASE III for creating and using such a file.

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