Architectures for Multi-Tier Development The various multi-tier development
Architectures for Multi-Tier Development The various multi-tier development architectures are: . HTML-based architecture . XML-based architecture HTML-Based Architecture HTML-based architectures map to the architecture as shown below: In the diagram you can see an approximation of a multi-tiered architecture. The three layers are visible and we’ve also pictured the abstraction for the presentation language and different storage options available. Alternatively, you could build a database cluster at the back end for your databases. The database then has to be enabled to work among the cluster of servers. The Content Layer The content layer abstracts the data modeling language being used. There are usually two different components in this layer: . The Access Component . The Data Manipulation Component The Access Component The access component abstracts the storage method being used and provides basic primitives for storing, retrieving, and manipulating data. If you use files you will not have an access component. If you use XML then you can have an access component to store and retrieve XML files so that you can easily use a file system, a repository, or the Web to store XML files without changing to other modules. If you use databases then the access component is a class abstracting the database being used. It provides functions to connect, query, and process results from the database. If you decide to change your database then all you need to do is to change this class without modifying the code that uses it. The Data Manipulation Component The data manipulation component is a client of the access component. This is where you will place all the functions needed to manage the data model, get data, store data, delete data, update data, insert data, and so on. The data manipulation component also handles the integrity and referential integrity of the data. Modules in this layer are not responsible for checking data to be consistent with the logic of the application since this will be handled at the logic layer. The Logic Layer The logic layer will be represented by a set of classes, each encapsulating different business rules or logical components. The functionality of the whole system will be coded in this layer. The logic layer uses the content layer to retrieve data to be manipulated. It will query the data model and update according to the logic specific to the application. The logic layer also uses the presentation layer to present the data after it has been manipulated. The Presentation Layer In the presentation layer you will find all the functions needed to present data to the client. You can divide this layer into two components: . The presentation language component This component encapsulates presentation functions according to the presentation language being used, say HTML. When an abstract presentation feature is needed, you just add it to the presentation language component. . The data presentation component Page 534
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