望文生义：
Repository [rɪˈpɑzəˌtɔri]
释义：仓库,贮藏所,受人信托的人,心腹,亲信
Repository模式可以称为仓储模式，或资源库
大师解释：
by Edward Hieatt and Rob Mee
Mediates between the domain and data mapping layers using a collection-like interface for accessing domain objects.
A system with a complex domain model often benefits from a layer, such as the one provided by Data Mapper, that isolates domain objects from details of the database access code. In such systems it can be worthwhile to build another layer of abstraction over the mapping layer where query construction code is concentrated. This becomes more important when there are a large number of domain classes or heavy querying. In these cases particularly, adding this layer helps minimize duplicate query logic.
A Repository mediates between the domain and data mapping layers, acting like an in-memory domain object collection. Client objects construct query specifications declaratively and submit them to Repository for satisfaction. Objects can be added to and removed from the Repository, as they can from a simple collection of objects, and the mapping code encapsulated by the Repository will carry out the appropriate operations behind the scenes. Conceptually, a Repository encapsulates the set of objects persisted in a data store and the operations performed over them, providing a more object-oriented view of the persistence layer. Repository also supports the objective of achieving a clean separation and one-way dependency between the domain and data mapping layers.
个人理解：
1，Repository主要是用来隔离domain与持久层， 就像是一个存储在内存中的domain对象集合 。
2, 方便测试，因为可以把针对数据库的持久化操作替换成内存中操作，解除对数据库依赖。
3, 数据存取集中放在一起，方便阅读和维护。
如，现在要对数据存取加上缓存功能。只要统一修改Repository层即可。
参考：
http://martinfowler.com/eaaCatalog/repository.html
http://msdn.microsoft.com/en-us/library/gg416511(VS.98).aspx