  With the advent of Web 2.0, an increasing number of web sites has started
offering their data over the web in standard formats and exposed their
functionality as APIs. A new type of applications has taken advantage of the
new data and services available by mixing them, in order to generate new
applications fast and efficiently, getting its name from its own architectural
style: mashups. A set of applications that aims to help a user create, deploy
and manage his mashups has also emerged, using various approaches. In this
paper we discuss the key factors that should be taken into consideration when
designing a mashup creator, along with the most important challenges that offer
a field for research.
