A couple of definitions

3-Tiers Application

Presentation Tier
Middle Tier
Data Tier

Middle Tier is further decoupled into following sub layers:

DAL - Data Access Layer
BLL - Business Logic Layer
Shared Components (such as Validation, Authentication etc.)

Data Tier is refered to database schema, stored procedures and so forth.



RESTful Service
Referered to Reprentational State Change, It sees a service as combination of resources and access verbs. A RESTful service is considered stateless treated as Datasource like a database.

Resource are represented by URLs and accessing verbs are by Http verbs.

Lo-REST (GET and POST)
Hi-REST - (DELETE, PUT as well)

The question is that do you trust your client to perform this critical operations? The answere is that it depends the application environment, the clients are preauthorized or not.

WADL - Web Application Description Language, it is the RESTful version of WSDL.