Frequently Asked Questions

STREAM Online Help > Frequently Asked Questions

1. Q: I got to the "Stream Visualizer - Connect" screen, hit OK (with the default options, as per the instructions). Then I got an error message stating that the client was unable to connect with the server. (E.g., the screenshot of the window generated looks like this.)
   
   A: You might be behind a firewall or NAT. Try checking the "Check here if you are behind a firewall or NAT" checkbox on the "Stream Visualizer - Connect" screen as shown here. We will then use a tunneling proxy on our side to pass all traffic between the client and the stream server through the web server frontend used by our system.
2. Q: What is Java Web Start? How do I get it to work with my browser?
   
   A: Details are available here.

3. Q: What is CQL? Where can I learn more about CQL?
   
   A: Queries in the STREAM system are expressed in the CQL (Continuous Query Language) declarative query language for data stream systems. A quick introduction to CQL is available here. This page also contains more references on CQL.
4. Q: When I attempt to register a CQL query, I get a parse error or a semantic error. Where can I find the CQL syntax and semantics specification?
   
   A: The authoritative source on CQL query syntax supported currently by STREAM is available here. This document also lists the semantic checks done by the STREAM CQL query parser.
5. Q: How do I interpret the query results? What are the different query output formats?
   
   A: Results can be reported back in one of the following formats:
   1. In a scrollable tabular format (default) with the result tuples displayed in increasing timestamp order from bottom to top of the results window. That is, more recent tuples are displayed on top. The results window is configured to display the 10,000 most recent updates to the query result. Once the number of result updates so far exceeds 10,000, the oldest ones are dropped from the bottom of the scrollable results window.
   2. A graph of the number of result tuples received at the client per second. For this format you need to check the "Statistics only" box.
   3. Printed to a local file by checking the "Write to File" box. You will be prompted for the file name.