4.3 扩展性
NCSTRL为我们在扩展性方面提供了很好的经验。由于NCSTRL的成员单位比较分散，并且不断有新的成员单位及新的用户加入，最终选择了把数字图书馆划分成不同的区域，这样不但适应了数字图书馆不断延伸的特点，而且还能为本地用户提供及时的、具有本地特色的服务。在中国数字图书馆工程建设一期规划（2000—2005）就采用了区域服务的思想。
4.4 伸缩性
由于各数字图书馆建设单位在经
济、技术、管藏资源、用户需求等方面都不平衡，因此不同数字图书馆的建设规模也将是不同的。一个好的体系结构设计必须能够适应不同规模的系统，使不同规模的系统都能够获取最佳的效率。
【参考文献】
[1] William Y. Arms etc, An Architecture for Information in Digital Libraries,D—Lib Magazine, February 1997 http://www. dlib. org/dlib/february97/cnri/02armsl, htm
[2] C. Lagoze （ed.）, W. Arms, S. Gan, D. Hillmann, C. Ingram, D. Krafft, R. Marisa, J. Phipps, J. Saylor, and C. Terrizzi. Core services in the architecture of the National Digital Library for science education NSDL）. In Proceedings of the Second ACM/IEEE—CS Joint Conference on Digital Libraries, Portland, OR, 2002.
[3] D. Fulker and G. Janee. Components of an NSDL architecture: Technical scope and functional model. In Proceedings of the second ACM/IEEECS Joint Conference on Digital Libraries. Portland. OR. submitted in January 2002.
[4] William Y. Arms, Diane Hillmann etc. A Spectrum of Interoperability The Site for Science Prototype for the NSDL, D—Lib Magazine January 2002 http ://www. dlib. org/dlib/january02/arms/01arms, html
[5] Dushay, N. , J. C. French, and C. Lagoze, “A Characterization Study of NCSTRL Distributed Searching,” Cornell University Computer Science, Technical Report TR99—1725.January 1999
