Separate speaker notes to accompany the separate PowerPoint presentation on data:
This presentation will deal with the storage of data both in files and tables.
Note that when you are talking about databases, the data shown here in a file would be called a table. A database contains many tables of information. Before databases, collections of information stood alone and were called files. With the advent of a database the vocabulary changed. The database can hold many collections of information under the database umbrella. These collections are now called tables.
Note that all of the records on the file have the same structure. That is they have the same fields in the same order and the fields are the same length. The data is also of the same type. This is because when a file is developed we define the structure of the file.
Again note that files are made up of records. In this example, each record is about a particular book. The record is made up of fields to hold the information about the book.
With most files, you define a unique identification number. If you go in an ask for the record with that identification number you will get one and only one record. This is called the key. In our example, the ISBNNo is the key.
Text or string or character data is data that is not going to be used in mathematical calculations. Numeric data is stored as a number. In most languages you need some type of designation to establish whether the type of number. For example is it an integer or decimal number. Numeric types can be very sophisticated for different mathematical needs.
Please note that in my chart, I referred to the ISBN#, but when I set up the structure of the file, I called it ISBNNo. You should not use special characters except the hyphen or the underscore when defining names. Most languages allow for either the hyphen or the underscore but not both. You should never make an embedded space part of a name.
Using a change of case makes the new word stand out.
Note that Access allows many of these rules to be broken. For example, Access allows embedded spaces. NO NOT USE EMBEDDED SPACES IN NAMES OF FIELDS. It is a bad habit to get into and causes complications even within Access.
At this point, do not worry about the COBOL syntax. Just note that there is a BOOK-RECORD with 5 fields. Each field has a name, a type and a length.
This slide shows the booklist table in the asgn1 database. Note that in previous slides I described the data as a file because it was standing alone. Now I am describing the data as a table because it is part of a database.
The field isbn is given a data type of text and a field size of 13. I also highlighted it and clicked on the key icon to make it the primary key (unique identification number).
In Access, instead of setting the number of characters for numeric fields, I choose a type. Access has an allotted number of characters for each type I choose. If you are interested in the details, you can find information in help.
This shows the data that was entered into the booklist table structure. Visually you can see why it is called a table, the rows are records and the columns are fields, giving it a table like appearance.