what is an information system?

1) "what is an information system?"
在網上可以找到的定義，例如：
在 http://www.thefreedictionary.com/information+system 可找到...
Information System - system consisting of the network of all ommunication channels used within an organization
在 http://en.wikipedia.org/wiki/Information_systems 可找到...
Information Systems is the discipline concerned with the development, use, application and influence of information technologies. An information system, following a definition of Langefors, is a technologically implemented medium for recording, storing, and disseminating linguistic expressions, as well as for drawing conclusions from such expressions.
在 http://www.pcmag.com/encyclopedia_term/0,2542,t=information+system&i=44963,00.asp 可找到...
information system - A business application of the computer. It is made up of the database, application programs and manual and machine procedures. It also encompasses the computer systems that do the processing.

網上找到定義可謂五花八門，而我自己的定義就是：
The management, planning, implementation and the use of information technology, such as computer, networking and database application to fulfil a company's business goal.
這是我十多年前一所英國大學裡的博士所說的，當然我上述的字眼未必與他所說的是一模一樣，不過意思就是這樣了。
2) "differentiate information system with information technology??"
我自己認為IS和IT的分別就是...
IS就是Planning，而IT 就是Execution...
例如IS發現一個opportunity，公司在某些方面利用電腦化的資料庫系統會增加運作效率、減低成本 (當然整個project要在公司允許的budget內能實現的)，IS便會做一些research，按公司和user的需要設計一個Database application的database structure, data flow diagram(DFD), etc，而IT的programmer就會利用programming languages去develop個application system.
IS與IT 的關係就和 QA與QC的關係差不多，QA就是計劃公司對品質有關和有影響的一切活動，而QC就是QA計劃中的其中一個活動去檢查產品/工序的質量。
你問得這條問題，我估都是為了滿足工課上的需要吧，多上網找資料看看，或找本參考書，當然歡迎你加入的見解，然後你才去回答你上述的問題啦。

Information Systems is the discipline concerned with the development, use, application and influence of information technologies. An information system, following a definition of Langefors, is a technologically implemented medium for recording, storing, and disseminating linguistic expressions, as well as for drawing conclusions from such expressions.
The technology used for implementing information systems by no means has to be computer technology. A notebook in which one lists certain items of interest is, according to that definition, an information system. Likewise, there are computer applications that do not comply with this definition of information systems. Embedded systems are an example. A computer application that is integrated into clothing or even the human body does not generally deal with linguistic expressions. One could, however, try to generalize Langefors' definition so as to cover more recent developments.
One of the better descriptions of this discipline came from Alan Lee, "...research in the information systems field examines more than just the technological system, or just the social system, or even the two side by side; in addition, it investigates the phenomena that emerge when the two interact." Lee AS (2001) "Editor’s Comments" MIS Quarterly 25(1), iii-vii
For more details, pls click
http://en.wikipedia.org/wiki/Information_systems