Google plans to enhance its online spreadsheet apps, including the ability to display data in new ways using lightweight "gadgets" and to notify users via email when data is changed.

The enhancements, expected to appear today, will be extended later to the other Google Docs components -- the word processor and presentation applications.

The gadget feature will let third-party developers and Google create new features for the spreadsheet application, said Jonathan Rochelle, senior product manager for Google Docs.

"If we have a new idea for visualizing data, we can create that as a separate feature that can be pushed out to users of Google Docs' spreadsheet," he said.

For example, a gadget could be created that takes data from a spreadsheet and presents it visually on a map or in charts that can be displayed in sites that support inline frames, such as the iGoogle personalized home page, he said.

"We're finding today, spreadsheets being used more and more as a foundation to publishing information on websites," Rochelle said.

The gadgets will access spreadsheets via a visualization API, designed to let developers quickly identify a range of cells whose data they want the gadget to use or render graphically, he said.

Meanwhile, the new notification feature will generate email messages to users who collaborate on a spreadsheet, alerting them of changes to the document, including who made modifications and what changed.

The notifications, which users can configure to receive once per day or every time a change is made, also include a link to the spreadsheet, where the modified cells will appear highlighted, Rochelle said. "It supports the collaboration and makes it stronger," he said.

Google didn't say on Tuesday when the enhancements would be made to the other Google Docs programs.

Google Docs is a free suite of web-hosted applications that is considered a rival and a complement to Microsoft Office, the dominant office productivity suite. Unlike Microsoft Office, which is designed for desktops, Google Docs is a software as an online service model that’s strong on collaborative features.

People can sign up for Google Docs only, or they can use it as part of a broader collaboration and communication suite called Google Apps, which includes other components like Gmail, Google Sites and Talk.