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Documentation/FAQ
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Frequently Asked Questions about GZigZag, with answers.
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$Id: FAQ,v 1.7 2001/02/09 05:59:36 ajk Exp $
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All trademarks are the trademarks of their respective owners.
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Note that the 'I' in this document is Tuomas Lukka.
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=============================================================
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Section I: General questions
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1. Where to get the latest version of this FAQ?
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The source code for all versions of this FAQ is kept as a part of the
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GZigZag CVS repository. See the GZigZag sourceforge page at
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http://gzigzag.sourceforge.net
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for accessing the source. The FAQ is in the directory Documentation/
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-----
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2. What is ZigZag?
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ZigZag, an invention of Ted Nelson, is a new type of data structure.
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For mathematicians, the key words would be
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- discrete
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- multidimensional
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- locally euclidean
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- with global directions (coordinate axes)
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and for non-mathematicians, these are explained below:
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Discrete:
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the information is stored in cells, kind of like a
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spreadsheet.
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Multidimensional:
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instead of two dimensions, X and Y, that a spreadsheet
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has, a ZigZag space can have any number of dimensions
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which are distinguished by strings.
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Locally Euclidean:
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a spreadsheet is globally euclidean, i.e. it is a lattice.
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ZigZag is only locally euclidean, so the neighborhood of
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(i.e. the cells next to) a given cell looks euclidean:
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if you go up and come down, you are back where you were before.
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But if you start from location 1, and go up, left, down and
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right, you might not get back to where you were, let's
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say you are at location 2. But if you then go left, up, down
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and right from location 2, you get back to location 1.
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The connections in ZigZag are user-alterable so you can
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connect any two cells along any given dimension, but
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because of the local euclidean constraint, each cell
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can be connected to only one cell in the positive and one
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cell in the negative direction on each dimension.
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Computer scientists might note that ZigZag is an interesting special
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case of graphs.
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-----
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3. What is GZigZag?
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GZigZag is an implementation of ZigZag developed by a research group led
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by Tuomas Lukka at the university of Jyvaskyla.
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It is licensed under the LGPL (and XPL, the Xanadu Public License which
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is still under works).
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-----
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4. Who is the maintainer of GZigZag?
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Tuomas Lukka, <lukka@iki.fi>. He has written most of the code in GZigZag (and
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most of it while traveling on trains).
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This maintainership is by proxy from Ted Nelson, who has the official
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maintainership but who does not program.
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-----
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5. How complete/stable is GZigZag?
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It's pre-alpha. It is already usable for many things but it is nowhere
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near feature complete yet.
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As for stability, crashes are quite rare but the development speed is high.
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-----
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6. What are some planned features?
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See Java/TODO in the distribution.
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-----
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7. Are there any mailing lists associated with ZigZag/GZigZag?
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See http://www.xanadu.com/zigzag
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-----
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8. How can I help?
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Email Tuomas Lukka <lukka@iki.fi> and ask.
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=============================================================
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Section II: Using (G)ZigZag
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1. How can I learn to create my own structures so that they work well?
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There are some ideas in the document "A Gentle Introduction to ZigZag",
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available under the
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Documentation/Gentle_Introduction
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directory on the CVS, or as a postscript file from the web page.
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=============================================================
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Section III: Questions specific to the Java version
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1. Why Java?
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Portability, garbage collection, SPEED (with JIT: for linux, IBM's
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JDK-1.1.8 is GREAT), portable graphics, easy C interface, available APIs
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(e.g. JMF), etc.
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You will note that I did not mention the language itself above:
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I don't like the language itself that much: I'd prefer to work in
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Perl. Unfortunately it does not provide all of these other features and
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the ones it does it does not provide as easily and conveniently as Java.
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-----
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1.1 Where do I get Java sources for GZigZag?
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If you know CVS, you can checkout module GZigZag in
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:pserver:anonymous@cvs.gzigzag.sourceforge.net:/cvsroot/gzigzag .
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Otherwise, you can use our nightly-generated source snapshots
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available at ftp://gzigzag.sourceforge.net/pub/gzigzag/snapshots/ .
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They are packaged in GNU-Zipped tar archives and in ZIP archives,
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choose whichever is best for you.
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The Java sources are located in the Java/ subdirectory of the full
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source tree.
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-----
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1.2 Where do I get precompiled class files for GZigZag?
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We have a build daemon that builds the current CVS version nighly and
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puts two JAR archives of it in
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ftp://gzigzag.sourceforge.net/pub/gzigzag/snapshots/ . The
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-without-modules version contains the core GZigZag. The -with-modules
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version is much larger and contains some additional functionality.
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-----
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1.5. It's WAY too slow! Are you out of your mind?
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No. For me, it's quite comfortable on my 233MHz Pentium 80Mb laptop.
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There are several possible reasons for this:
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* You are using a Java interpreter without a JIT (Just-In-Time)
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compiler. As mentioned in the answer to the previous question, for
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Linux, I recommend IBM's JDK 1.1.8. Do NOT ask me about proprietary
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operating systems - GZigZag works there but over there you're on
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your own for platform-specific questions. Another quite fast JVM is
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Kaffe, but unfortunately at least some versions of Kaffe have a
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nasty bug that makes using GigZag on it quite unpleasant.
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* Your Java interpreter is not using enough memory. By default, some Java
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interpreters only use 16Megs at maximum. Try starting with
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java -mx30m -ms30m foo.Main
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to set it to allocate 30Megs at startup (or more if you have enough memory).
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That way it won't be garbage collecting constantly and you may get quite a
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significant performance improvement.
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-----
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1.5.1. I can't use IBM's JDK: it doesn't have the Swing classes
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You are using an old version of GZigZag. Current CVS versions and
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snapshots do not require Swing.
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-----
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1.9. I want to report a bug; how do I do that?
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There are instructions about this in http://www.gzigzag.org/bugs.html .
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-----
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2. How is the Java code structured?
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ZZCell and ZZSpace are the center of it all. Start from there and
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also ZZDimension, ZZDimSpace, ZZLocalDimension, ZZPersistentDimension,
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ZZPersistentDimSpace ...
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These latter ones are still a bit new and finding their places.
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-----
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3. Why is the ZZEventQueue not called / what is ZZObs / ... ?
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Legacy. It's currently supplanted by the ZZUpdateManager for view updates
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but may be revived later.
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-----
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4. What is the saved file format?
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See the Java/storage/ and Java/media subdirectories of the source
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tree, especially storage/Recs.java, storage/ZZPersistentDimSpace.java
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and media/StringScroll.java.
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-----
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5. Will my files be upwards compatible?
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No: the format will change soon. However, you can dump the space into XML
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(will be explained later) and restore it to the new file type.
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-----
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6. Are there any coding standards?
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See the file CODING in CVS.
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-----
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7. Do you accept patches?
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Yes, we do, but it helps if you consult with us first to make sure your
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intended change is in a reasonable direction. Much functionality should go
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into the Modules/ as well.
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diff -u (unified diff) is preferred.
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-----
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8. What are the advantages of the new Java version over the old Perl version?
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- Graphics. You just need to see the vanishing view to see why it's important.
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And that's just the beginning.
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- Active development.
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-----
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9. What are the disadvantages of the new Java version over the old Perl version?
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- Ted's own keystrokes do not yet work (to be fixed soon)
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=============================================================
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Section III: Questions specific to the Perl version
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1. Wasn't there a Perl version or something?
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Yes, written by Andrew Pam and others.
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-----
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2. Are the files from the Perl version compatible with the new Java version?
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No.
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-----
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3. Is it possible to import files from the Perl version to the new Java version?
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Not yet, but soon. Only needs a short Perl script to read the DB_File from
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the Perl version and write the corresponding XML code and then you can import
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it.
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