In its most generic sense, the term application applies to a task. For example, a widget maker needs to take orders and transmit these orders to a warehouse where the widgets are shipped to customers. The widget factory and warehouse must exchange inventory information. This whole procedure might be called an order entry and inventory control application. In this sense, other applications include list management, accounting, design, marketing, and sales - the tasks of any enterprise.

More specifically, the term application refers to the computer software used to get a job done. Thus, database management packages such as dBase IV, Paradox, and Oracle are called application software, as are other types of software such as WordPerfect, Co/Session, and 1-2-3. In this sense, application software is distinguished from system software, which is the software that makes computers and networks operate. Think of the application software running on top and taking advantage of the system software and hardware.

Finally, application refers to programs written to perform a specific task. For example, many users have written applications in the dBase language. These customized applications are written by and for end users, not by software vendors. This can get tricky, because some value-added resellers and system integrators write such customized programs to sell. The difference is they are not selling generic applications software as Microsoft, Borland and Lotus do. They, like the end-users themselves, are creating customized programs using the software of developers such as Borland and Microsoft.

Network operating system software, such as NetWare, LAN Manager, and VINES, provide some applications. This presents some complications and indicates some changing directions for the PC network industry.

Networks exist for applications. That is, users install networks to get a job done. Users can have computers, cable, interface cards, file servers, and protocols, but without applications software users can't do much but copy files from disk to disk. Network application software is what people use. The network is just the substrate upon which they use it.

APPLICATION TYPES
There are three types of applications - network-ignorant, network-aware, and network-intrinsic.

Network-ignorant applications are written for use on one computer by one person. These programs can run on a network in the sense that they may be stored on a file server and network users may run them at their workstations. Most of the time there are severe limitations on what these applications can do. Moreover, if two people try to use the program at the same time, data can be lost or corrupted.

For example, if two people try to work on the same 1-2-3 spreadsheet, the person making the last change to the spreadsheet will write over all the changes made by the user who first saved his work. The program has no way of keeping the users from destroying each other's work. It lacks concurrency control. On the other hand, 1-2-3 can be used safely by several people at the same time, as long as they are using different spreadsheets (and if they have a license to do so). But the standalone version of 1-2-3 does not provide functions to take advantage of the network.

Network-aware applications are a step above network-ignorant applications. Usually, they are network-ignorant programs modified to run on a network. These programs recognize they will be used by several users at a time. They have concurrency control features such as file and record locking to coordinate usage by multiple users. For example, when a Paradox user begins to modify an address in a mailing list database, other users who are also looking at the same database table are prevented from changing that particular address record. This is called record locking. When the change is complete, the change is displayed on the screen of every other user looking at the table.

Another network-aware feature is file locking. This is a less sophisticated and less used form of concurrency control. Instead of keeping users out of a particular record, they are kept out of the entire file altogether while another user has it open. Word processing programs are the primary users of this type of concurrency control. Communications software and electronic mail are also network-aware applications. They use the network to extend the abilities of a PC and share network resources.

At the same time, even these network-aware applications use the network as little more than a peripheral sharing device. The file server holds the data and the program but does not do any processing. Users access the program as if it were local, but all the work is being done by their PC, including all concurrency control. This is changing.

Network-aware programs make up the vast majority of programs written for networks. They are a big improvement over network-ignorant applications and have gone a long way to spur the growth of networking. As they become more sophisticated, the distinction between network-aware and network-intrinsic is blurring.

NETWORK-INTRINSIC APPLICATIONS
Network-intrinsic applications actually share the processing power of several computers. Usually, although not always, this is done by dividing the application program into pieces. One piece is the server, which does data processing; the other piece is the client, which talks to the user. A database server is a good example of this application type. Its principles can be generalized for other network-intrinsic applications.

A database server is composed of front and back ends. The front end is responsible for formulating requests and displaying formatted data to the user. At the front end, users make queries, write reports, create new databases - all the tasks they do with any other database management program. The back end is responsible for managing and searching for data, concurrency control, and security. When a user asks for all the employees in the company database that make more than $50,000, this request is transmitted to the database server or back end. The database server then looks for all the employees making over $50,000 and sends these records to the front end.

In the network-aware method, one program, not two, runs in the user's machine. When the request for middle-income employees is made, the server downloads the entire file over the network to the user program. The user's PC then searches through the file to find the employees with the requested salaries. This takes up much more network bandwidth because the whole file is transferred, instead of just a few records. Other traffic includes concurrency control commands to lock various files and records as needed.

With a database server, concurrency control traffic is eliminated because the server takes care of it. Even more important, only the requested records are sent over the network. The result is a more efficient, safer, and better performing program and network. The two programs are working together to create one application - a true network-intrinsic application.