dBASE III
dBASE III mejoró la velocidad, la memoria y la facilidad de uso respecto de dBASE II, incorporando menús y nuevos tipos de ficheros.
It is a relational-type database. Let us look at the hardware requirements and some characteristics:
Microprocessor: 8088, 8086.
Minimum memory: 256 Kbytes.
Operating system: MS-DOS, PC-DOS 2.0 (and higher), UNIX.
Characteristics:
Maximum number of fields per record: 128.
Maximum number of characters per record: 4000.
Maximum number of records per file: 1,000,000.
Maximum number of files opened simultaneously: 10.
The introduction of dBASE II into the market represented a major step forward in bringing databases closer to personal computers.
Although it was generally well received in computing environments, it also received criticism. These criticisms stemmed from its slow processing speed and the limited size of databases it supported. Non-programmers complained about the difficulty of its programming language (and consequently, its use). dBASE II worked with 8-bit microprocessors; dBASE III uses a 16-bit one.
A 16-bit microprocessor has the advantage of processing data more quickly than an 8-bit one; in addition, its use has become widespread. Although developed from dBASE II, dBASE III is completely different from its predecessor. However, given the power of the language it includes, it is difficult to master it thoroughly and take full advantage of its capabilities.
The main differences are:
It uses a 16-bit microprocessor.
Processing speed is higher.
It has greater memory capacity.
It is easier to become familiar with.
One of dBASE II’s shortcomings was its difficulty of use, as it did not work with menus. dBASE III incorporates menus, making it relatively easy to become familiar with it in a short period of time.
One way to manipulate information in a data file is through iterative instruction processing. This consists of entering dBASE III-specific commands through the keyboard. After entering a command, the results appear on the screen.
Another way to process information in dBASE III is batch instruction processing (what we previously referred to as programs). The operations to be performed are defined beforehand as a set of instructions, which are then executed all at once. These instructions are stored in an instruction file that can be considered a computer program.
The operations in the program can be selected through menus.
Once we have seen how dBASE III processes operations, we will examine a special feature of this database: it contains nine different types of files, depending on the nature of the information stored.
These are:
Database file. Contains the records and fields where data is stored.
Memo data files. Store large blocks of data.
Index files. Provide the necessary space for sorting a file. This allows access to data in an order different from the original.
Instruction file. Stores the set of instructions that will be processed.
Format file. Stores information specifying the output format of records.
Label files. Store information about labels that will be printed.
Memory files. Store the contents of memory variables. These represent temporary memory locations that can hold calculation results for use in later processes.
Report format files. Contain information needed to generate reports, which are produced using the REPORT instruction.
Output text files. Store text that can be shared with other computer programs. They allow the links needed for the exchange of information between dBASE III and external systems.
