Mashups are still relatively new to the technology world, but little by little, it seems they are picking up steam among enterprise businesses.

While their definitions are still somewhat shadowy and standards are still quite a ways off, mashups are defined in some generally accepted ways: presentation, process and data mashups. J. Jeffrey Hanson, author of "Mashup Patterns: Designs and Examples for the Modern Enterprise," describes the three main categories:

Presentation mashups: "A presentation layer mashup deals mainly with user interface artifacts," Hanson said. "Alot of things that can be created with widgets, JavaScript, HTML snippets, DOM manipulation and that sort of thing."
Process mashups: "These are more of an IT operation, with inter-process communication and message queues. It's more of a traditional source code integration."
Data mashups: "Mashups that are integrated at the data level, whether it's integrating files, databases, external Web service APIs."  

These categories were also noted by companies providing mashups, including Serena and JackBe. No doubt as mashups continue to evolve, these three categories will intertwine, and we will likely even see other forms of mashups being spawned. When asked what the challenges are in bringing mashups to the enterprise level, Hanson said ensuring privacy and making sure data and identities are secure can be the most tricky parts. Additionally, governance needs to be addressed right away because mashups are a public model with company information exposed in the public realm.