Event data (e.g., log messages) are represented as sets of attribute/value pairs. An index maps each attribute/value pair or attribute/value tuple to a pointer that points to event data which contains the attribute/value pair or attribute/value tuple. An attribute co-occurrence map or matrix can be generated that includes attribute names that co-occur together. Queries and custom reports can be generated by projecting event data into one or more attributes or attribute/value pairs, and then determining statistics on other attributes using a combination of the inverted index, the attribute co-occurrence map or matrix, operations on sets and/or math and statistical functions.