Excel Services Architecture
Published: May 2010
Excel Services is part of Microsoft SharePoint Server 2010. Excel Services is built on ASP.NET and SharePoint Foundation technologies. Following are the core components in Excel Services:
Excel Web Access
Excel Web Services
User-defined functions (UDFs)
Representational State Transfer (REST) service
Excel Calculation Services
Microsoft Excel Web App, part of Microsoft Office Web Apps, also supports Excel workbooks in the browser. For more information about Excel Web App, see documentation about Office Web Apps.
In the simplest configuration in SharePoint Server 2010—that is, a single computer running SharePoint Server 2010 as a stand-alone installation—all five components are installed on the same computer. However, in a typical enterprise environment with a large number of users, the components on the Web front-end server and the components on the back-end application server are on different computers in a farm configuration. It is possible to scale out the Web front-end server independently from the back-end application server. For example, you can have more Web front-end servers or more back-end application servers, depending on your organizational needs.
Excel Web Access is a viewer page and an Excel Services Web Part that you can add to any Web Parts page in SharePoint Server 2010. Excel Web Access renders (in other words, creates the HTML for) live Excel workbooks on a Web page, and enables the user to interact with those workbooks and explore them. Excel Web Access is the visible Excel Services component for the user. You can use Excel Web Access like any other Web Part in SharePoint Server 2010. Excel Web Access does not require the user to install anything on the client computer.
The Excel Web Access Web Part properties are also customizable. For more information, see the namespace reference documentation.
Excel Web Services is the Excel Services component that provides programmatic access to its Web service. You can develop applications that call Excel Web Services to calculate, set, and extract values from workbooks, and to refresh external data connections. By using Excel Web Services, you can incorporate server-side workbook logic into an application, automate the updating of Excel workbooks, and create application-specific user interfaces around server-side Excel calculation.
When you make changes to a workbook—for example, by setting values to a range by using Excel Web Services—the changes to the workbook are preserved only for that session. The changes are not saved or persisted back to the original workbook. When the current workbook session ends (for example, when you call the CloseWorkbook method, or when the session times out), the changes that you made are lost.
If you want to save changes that you make to a workbook, you can use the GetWorkbook method, and then save the workbook. For more information, see Microsoft.Office.Excel.Server.WebServices. You can also open the workbook in edit mode and save the changes.
For more information about Excel Web Services, see Excel Services Development Roadmap.
Excel Services UDFs enable you to use formulas in a cell to call custom functions that are written in managed code and deployed to SharePoint Server 2010. For more information about UDFs in Excel Services, see Understanding Excel Services UDFs.
The REST API in Excel Services enables you to access workbook parts or elements directly through a URL. The URL contains a "marker" path, which is the entry point to an .aspx page, to the workbook file location, and to the path to the requested element inside the workbook.
The discovery mechanisms built into the Excel Services REST API enables developers and users to explore the content of a workbook manually or programmatically.
For more information about the REST API in Excel Services, see Excel Services REST API.
The role of Excel Calculation Services is to load workbooks, calculate workbooks, call custom code (UDFs), and refresh external data. It also maintains the session state for interactivity. Excel Calculation Services maintains a session for the duration of interactions with the same workbook by a user or caller. A session is closed when the caller explicitly closes it or when the session times out on the server. Excel Services caches the opened Excel workbooks, calculation states, and external data query results, for improved performance when multiple users access the same set of workbooks.
In multiple-server configurations, Excel Services load-balances requests across multiple Excel Calculation Services occurrences in a farm configuration. If your installation includes multiple application servers, Excel Services will balance the load in an attempt to help ensure that no single application server is overloaded by requests.
Administrators can configure the load-balancing behavior.