A Mashup is an applications combining and merging information in ways which may, or may be not, be the ones intendend by the site(s) where the information where collected in the first place. With mashups, the focus shifts from the application to the information which populate it. To make it brief: information rule

Hip-hop lent this term to Web 2.0, because originally mashup meant to produce a new song by mixing two or more existing pieces. As Wiki says, mashups currently come in three general flavors: consumer mashups, data mashups, and business mashups.

The most well-known type is the consumer mashup, best exemplified by the many Google Maps applications. Consumer mashups combine data elements from multiple sources, hiding this behind a simple unified graphical interface.

Other common types are “data mashups” and “enterprise mashups“. A data mashup mixes data of similar types from different sources, as for example combining the data from multiple RSS feeds into a single feed with a graphical front end. An enterprise mashup usually integrates data from internal and external sources - for example, it could create a market share report by combining an external list of all houses sold in the last week with internal data about which houses one agency sold.

A business mashup is a combination of all the above, focusing on both data aggregation and presentation, and additionally adding collaborative functionality, making the end result suitable for use as a business application.

Mashups and Portals are both content aggregation technologies. Portals are an older technology designed as an extension to traditional dynamic web applications, in which the process of converting data content into marked-up web pages is split into two phases - generation of markup “fragments” and aggregation of the fragments into pages. Each of these markup fragments is generated by a “portlet”, and the portal combines them into a single web page. Portlets may be hosted locally on the portal server or remotely on another server.

Portal technology defines a complete event model covering reads and updates. A request for an aggregate page on a portal is translated into individual read operations on all the portlets that form the page (”render” operations on local, JSR 168 portlets or “getMarkup” operations on remote, WSRP portlets). If a submit button is pressed on any portlet on a portal page, that is translated into a single update operation on that portlet alone (”processAction” on a local, JSR 168 portlet or on a remote, WSRP portlet). The update is then immediately followed by a read on all portlets on the page.

Portal technology is about server-side, presentation-tier aggregation. It cannot be used to drive more robust forms of application integration such as two-phase commits.

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