Chapter 13
There are many types of application system and, on the surface, they may seem to be very different. However, after examining the architectural organisation of applications many of these superficially dissimilar applications have much in common. There are four broad types of architectures discussed in the book:
Data-processing applications. These are data-driven applications, they process data in batches without explicit user interventions during the processing. The specific action taken by the application depend on the data that it is processing. Applications of this type are commonly used in business, where similar operations are carried out on a large amount of data. The nature of data-processing systems where records or transactions are processed serially with no need to maintain state across transactions means that these systems are naturally function-oriented. Functions are components that do not maintain internal state information from one invocation to another.
Transaction-processing applications. These are database-centred applications that process user requests for information and that update the information in database. These are most common type of interactive business systems. They are organised in such a way that user actions can’t interfere with each other and the integrity of the database is maintained. To simplify the management of different terminal communication protocols, large-scale transaction-processing systems may include middleware that communicates with all types of terminal, organises and serialises the data from terminals, and sends that data for processing. Implementations of information and resource management systems based on Internet protocols are now the norm.
Event-processing systems. This is a very large class of application where the actions of the system depend on interpreting events in the system’s environment. These events might be the input of a command by a system user or a change in variables that are monitored by the system. Real-time systems also fall into this category. However, for real-time systems, events are not usually user interface events but events associated with sensors or actuators in the system.
Language-processing systems. These are systems where the user’s intensions are expressed in a formal language (such as Java). The language-processing system processes this language into some internal format and then interprets this internal representation. The best known language-processing systems are compilers, which translate high-level language programs to machine code. In the very abstract way the language-processing system’s process can be described as: instructions go to the translator, which checks syntax and semantics and then generate some abstract instructions for interpreter. Interpreter takes those instructions along with data, executes the program and gives the output. Other components might also be included that transform the syntax tree to improve efficiency and remove redundancy from the generated machine code.
