随着数字图书馆的发展，各种资源间的互操作性也变得越来越重要，人们也一直致力于对分布式资源进行统一检索的开发。要实现这一目标，归纳起来有三种方式：代理模式，即通过检索代理对不同的目标源分别检索，然后对检索结果统一处理；联邦检索模式，即各个目标源严格遵守统一标准或协议从而实现底层的跨库检索；采集模式，即通过元数据采集协议将分布的元数据集中提供检索。本文对这三种模式进行了对比介绍，并对国际上应用越来越广泛的OAI元数据互操作机制及应用进行了详细介绍和讨论。

The interoperability of digital libraries is becoming more and more important with the development of digital resources. Generally, three types are categorized for current DL interoperability: Gathering, Federated and Harvesting. Each type has its advantages and disadvantages. Gathering translates the user query into acceptable queries for each DL and merges the hits into one page that is presented to the user. In harvesting approach, a service provider harvests metadata from data providers using a predefined protocol. Federated type needs all participants use the same DL protocol such as Z39.50. These approaches are compared briefly and particularly federated approach using OAI protocol is discussed.