# API Overview

Hyperion Essbase provides an online analytical processing (OLAP) solution that satisfies the complex calculation requirements of end-user analysts across the enterprise in various departments, including financial, accounting, and marketing. Essbase operates in a client-server computing environment on a local area network (LAN). This environment enables multiple users to retrieve and analyze centralized data with the personal computers they use every day.

Essbase client tools provide access to centralized data through a variety of interfaces, including:

- Spreadsheet interfaces.
- Application and data management facilities.
- Custom programs you can develop using the Hyperion Essbase Application Programming Interface (API).

The Hyperion Essbase API provides a range of powerful and sophisticated features, including:

- Transparent client-server access
- Data manipulation, consolidation and reporting
- Encapsulated server login procedure
- Remote file management
- Application/database administration
- User/group administration
- Transparent, built-in security
- Customized memory and message handling
- Multiple platform support
- Function library that allows direct creation, manipulation, and maintenance of Essbase outlines from a C or Visual Basic program
- For a list of new features, see Migrating Essbase API Programs

The API is an interface between your custom client program and the Essbase server and manages the transfer of data between client and server over the network. Your program makes calls to functions within the API, and data is returned from the Essbase servers you connect to. The Essbase API contains the same routines that Hyperion Software uses internally.

You can also run custom programs on the server machine, using the same API functions as on the client. In general, you don't have to be concerned about where the Essbase server machine is located on the network when writing a custom API program. Locating the server and transferring the data is all handled by the API.

The way your custom application accesses an Essbase server is shown below:

Before you write programs for the API, use this document to become familiar with some of the concepts and conventions it uses. You can familiarize yourself with these by reading the overviews in this document, preferably before you begin to write or adapt your program to work with Essbase.

The API provides all the functionality described in this document through header files that you include in the source code of your program and a set of libraries that you link to your program. C programmers might want to print out any relevant header files for easy reference.

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