Blog entry by HENDRO EKO PRABOWO 5116201006
All systems that involve interaction with a shared database can be considered to be transaction-based information systems. An information system allows controlled access to a large base of information, such as a library catalog, a flight timetable, or the records of patients in a hospital. Increasingly, information systems are web-based systems that are accessed through a web browser.
Picture 1. a very general model of an information system. The system is modeled using a layered approach where the top layer supports the user interface and the bottom layer is the system database. The user communications layer handles all input and output from the user interface, and the information retrieval layer includes application-specific logic for accessing and updating the database. As we shall see later, the layers in this model can map directly onto servers in an Internet-based system.
Picture 1. Layered Information System Architecture
As an example of an instantiation of this layered model, Picture 2. shows the architecture of the MHC-PMS. Recall that this system maintains and manages details of patients who are consulting specialist doctors about mental health problems. The detail added to each layer in the model by identifying the components that support user communications and information retrieval and access :
1. The top layer is responsible for implementing the user interface. In this case, the UI has been implemented using a web browser.
2. The second layer provides the user interface functionality that is delivered through the web browser. It includes components to allow users to log in to the system and checking components that ensure that the operations they use are allowed by their role. This layer includes form and menu management components that present information to users, and data validation components that check information consistency.
3. The third layer implements the functionality of the system and provides components that implement system security, patient information creation and updating, import and export of patient data from other databases, and report generators that create management reports.
4. Finally, the lowest layer, which is built using a commercial database management system, provides transaction management and persistent data storage.
Picture 2. The Architecture of The MHC-PMS
Information and resource management systems are now usually web-based systems where the user interfaces are implemented using a web browser. For example, e-commerce systems are Internet-based resource management systems that accept electronic orders for goods or services and then arrange delivery of these goods or services to the customer. In an e-commerce system, the application specific layer includes additional functionality supporting a ‘shopping cart’ in which users can place a number of items in separate transactions, then pay for them all together in a single transaction.
The organization of servers in these systems usually reflects the four-layer generic model presented in Picture 1. These systems are often implemented as multi-tier client server/architectures :
1. The web server is responsible for all user communications, with the user interface implemented using a web browser
2. The application server is responsible for implementing application-specific logic as well as information storage and retrieval requests
3. The database server moves information to and from the database and handles transaction management.
Using multiple servers allows high throughput and makes it possible to handle hundreds of transactions per minute. As demand increases, servers can be added at each level to cope with the extra processing involved.
Source : Sommerville, Ian. 2011. Software Engineering. 9th Ed. Boston: Pearson Education, Inc.