Here is a survey that is interesting
link to survey about xref tools

Wow, this is cool Susan Elliott Sims Homepage has some interesting things on it.

tandard Exchange Format
There is a movement originating in the reverse engineering community to create a standard format for exchanging data about software. This data can come from the program code directly or from other sources, such as the configuration management system and external documentation. I co-chaired a workshop, WoSEF (Workshop on Standard Exchange Format), at ICSE 2000 on this topic. So far we have approximately a dozen groups who have committed to using GXL as a common format. A tutorial and workshop on GXL were held at CASCON2000.

A related effort is the Waikiki Beach Club home page and mailing list. CSER has also held discussions on this topic in the past.
Source Code Searching using grug
My Master's work was the design and prototype of a tool called grug, grep using GCL. Software Bookshelf focuses on presenting architectural views of a a software system, and consequently the information about a system stored in the Books extends only to the file level. While this view is appropriate for architectural comprehension, lower level information is necessary for coding and debugging. My tool was based on grep, but will also use the semantic information about variables, procedures, etc. that is already available in Software Bookshelf. Janice Singer of NRC and Tim Lethbridge of University of Ottawa have made some good observations about grep and put them together in a paper and web site.

As part of this research, I conducted a survey on the habits of programmers as they search source code. This survey will help identify the searches that the tool must support in order for it to be considered useful and usable. The results have been written up in a paper that was accepted for publication in IWPC98.