EIS InfoBook Multi-[name] description, undated

NYC 9/11 Public Portal Document

automatically extracted and made available for an upload to a communications server to update another site's resident database. This effectively forms a replication capability within this distributed network. The distributed network’s principle reason for being is to support low bandwidth communication of specific data inserts and updates among a series of sites. This provides a reasonably robust form of data exchange at specific intervals of modest frequency. It is satisfactory for a system that lacks the communications connectivity necessary for the next type of architecture, client/server.

Two-Tier Client/Server Architecture

We define client/server computing as involving two or more computers that share tasks as part of a complete application. The design of the system optimally allows each computer to perform tasks that are appropriate to its capabilities and specific function. This suggests that computer resources and data storage resources are positioned where they will do the most good in fulfilling the application being performed.

Our two-tier client/server architecture, shown in Figure 2, is the system of choice when (a) everyone on the network needs to be sharing the same data and (b) the communications channels within or among sites have sufficient bandwidth to carry out an intense and continuous exchange I i of data. The downside of this ^£1 architecture is that when communication lines are down, Figure 2 remote sites have no computing capability. In many instances, this two-tier client/server architecture forms the most efficient way to exchange information and has a much lower system-wide maintenance. In the two-tier client/server, the database server contains all the data and many of the data retrieval rules. At the client workstation, the presentation GUI and the application reside in what is called a “thick" client. The GUI and application program must be maintained on each client with the application making requests to the server for data to be delivered to the client for display. Each

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