Coming to Terms: Three-Tier Architecture

ASPs often describe their software as having a "three-tier architecture." What does this mean? How does a recruiter using a Hiring Management System delivered by an ASP benefit from such architecture?

ASPs (application service providers) offer enterprises access to applications over the Internet. A Hiring Management System (HMS) is software that assist recruiters in managing all aspects of the recruiting process, from the requisition, to sourcing, managing candidate data, assessment, collaboration, correspondence, and beyond. Most HMS also run the Careers page on the customer's corporate Web site, providing a searchable listing of open positions and candidate log-on capabilities. Because of the wide variety of tasks that HMS perform, specialized components handle different functions: a powerful database to store and retrieve thousands of candidate records; an expert system with the decision-making rules for screening and ranking; a graphical user interface (GUI) for presenting the information to both internal and external users.

An HMS with a three-tier architecture is organized with three independent layers or tiers, each of which can run on the same machine or all running on different machines. The three tiers reflect the specialized functions of a web-based enterprise application.

1. The presentation layer delivers the application to the end users on the Web.
2. The business logic layer contains and executes the rules that run the application.
3. The database layer manages the data required by the application.

The business logic layer is the middleman between the presentation layer and the back-end database. When a recruiter performs a task, his or her request first goes to the Web server, residing on the first tier. The Web server directs the request to the application server on the second tier, to be processed. In processing the request, the application server may query data from the database layer. The processed request is returned to the first level, the Web server, where the processed information is encoded into HTML, the language of the Web, and sent back over the Internet to the recruiter's browser.

Why three-tier?
A three-tier architecture is considered to be the most suitable architecture for large, Web-based enterprise applications. The partitioning of the application enables rapid design and development of the system. The modularity makes it easier to make changes to just one tier without affecting the others. Separating the functions into distinct tiers makes it easier to monitor and optimize the performance of each layer. Load balancing and adding more capacity can take place independently at each layer. Multi-tier architecture also makes it simpler to scale the system across multiple processors on different machines.

Understanding the technical intricacies of three-tier architecture is certainly not a requirement in order for a recruiter to utilize the functionality of an HMS. Yet it is worthwhile to be familiar with the language describing technology platforms, especially when evaluating vendors. Technology and technical terms have become an essential ingredient in recruiting and HR; recruiters need to be conversant in all aspects of their profession.