Microsoft Office Tutorials and References
In Depth Information
Understanding the Architecture
The Excel Viewer is a predefined Web page that has one instance of the EWA on it. It can be used to view
one workbook specified as a parameter on the URL.
The flow described in the basic example at the beginning of this chapter is an oversimplification. In
practice, when the web page is rendered on the WFE, the EWA has a small HTML file that is generated
quickly, without a call to the ECS. This small HTML file contains an iframe element and a progress
message. The iframe message is sourced back to the WFE, and it will do the more expensive
operation of actually opening the workbook through the ECS. The progress message is displayed until the
iframe comes back with the HTML for displaying the spreadsheet.
When a user performs an operation in the workbook, only the iframe is refreshed, without requiring a
postback of the entire page (which might have additional Web Parts and controls).
The Excel Web Services API
Excel Services exposes an API to allow programmatic access to its functionality. The API is exposed as
a web service on the WFE, and also enables applications running on the WFE to link with it locally, as
shown in Figure 3-7.
Whether you access Excel Services through the EWA or the API, the basic concepts of sessions, requests,
state management, publishing workbooks, loading workbooks on the server, accessing external data,
performing operations, and memory management are the same. With very few exceptions, the same
administrator settings apply for both the EWA and the API.
Custom
Application
Browser
EWA
API
Web Front End
ECS
Excel Services
Figure 3-7
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