The objective of data mining is to find regularities, or interesting patterns in large data sets, such as business transactions. More recently, there has been great interest in extending this work to structured data, such as graphs. The domain could be a database of molecular graphs, or the web graph, and the question could be to find subgraphs which occur frequently in the data. Algorithms usually list frequent subgraphs or other patterns. There are many different formulations of this problem. At this stage of the development of the field, it appears to be of some interest to put together a general picture of the different variants. In this talk we present an attempt towards this direction.