This article focuses on a basic understanding on what ATG is,and what are the main components of ATG.The target audience is people who are new to this technology.Now about the framework.ATG is a Java based Framework used to develop the applications on Web.ATG framework mainly works on the basis of three concepts Droplets, Form Handlers and Repository.In this technology whatever web applications that we are creating are developed as individual bean components and they are linked using a properties file.Precisely ATG is a component centric development platform.There are certain terms a person dealing with the FW will frequently come across,one such term is NUCLEUS, which is the core of ATG Fw.Nucleus is actually a term which is contextual.It can be considered as a collection of server side java beans and servlets.Used mainly for back end functionalites like handling HTTP requests,Db connectivity etc.In a different way we can say it is the nucleus that organizes the java beans, and registers each of the bean components with nucleus.Key benefits of Nucleus includes, a hierarchical namespace-Each component is arranged in a hierarchical structure, and every component has a unique name.So it is easy to refer to components.Nucleus components are pre-built so it is easy to build an application by just writing the properties file.Relationship with components and java beans can be defined using name-value pairs in the properties files.

                          Front ends are developed using JSPs, ATG provides a set of tags for this functionality, called DSP tag libraries.These tags helps in rendering the content dynamically by linking nucleus components directly to the JSPs.Each component in ATG is defined by a PROPERTIES FILE.While creating a component, a properties file is automatically created in the path. This file helps the nucleus to know which component can be used for which application.The properties file contains a listing of Name-Value pair for each bean.It is also called as a CONFIGURATION FILE which follows a key-value format.Normally the properties file contains the following parameters:
Java class :- A java class to which the component is an instance of and lists the property values for initialization.
File name :-The complete path of the component.
Scope of the component :- There are 3 general scopes
                 Global- The state of the components can be shared among all the users.
                 Session- The state of the components is separated for individual users.
                 Request- A separate component is available for each request.
                 Description :-A brief description about the component.
                 Maximum file size :- It indicates the maximum size of the file.

DROPLETS :- is a Dynamo Servlet bean used in ATG. The dsp:droplet tag is used to embed the contents of one jsp into another html file. It also allows a user to refer a nucleus component rather than another JSP file.There are many droplets used in ATG those are called built in or OUT OF THE BOX components.I would like to mention a few of them so that when you start going through some official training this knowledge will give you an edge.For-each droplet, Switch droplet etc are a few droplets which are OOTB.
FORM HANDLERS :- A form handler describes how to link form elements in JSPs with the properties of nucleus component. It is an important tool used for complex form processing.
REPOSITORY :- A repository is a data access layer. The user or developer can access the data using the repository and repository item interface.There are a few models of repositories used in ATG.They are SQL Repository, SQL profile repository, Composite Repository, Versioned Repository etc.Elaborating on these at this stage will make things more complicated.

Just try to keep these names in mind as of now.I will try to come up with a better article on ATG, where readers will get a better understanding on each of the terms mentioned over here.

Related posts:

1. ATG Tag Library:DSP Tags
2. Interview Questions:Basic ATG
3. How to Use RQL in JAVA,ATG
4. Droplet & A Repository Query
5. ForEach Droplet & its usage in DSP