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Re: [sgf-std] New SGF property: transposition / links

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  • Stuart A. Yeates
    Great idea Anro Is he plan to extend sgfc to cover this and optionally expand trees? ... The idea of common subtrees is very common in computer go. I m not
    Message 1 of 12 , Jul 29, 2008
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      Great idea Anro

      Is he plan to extend sgfc to cover this and optionally expand trees?

      ----

      The idea of common subtrees is very common in computer go. I'm not
      sure whether any of the computer go programs externalise their search
      trees though. May I suggest that his issue is also raised on the
      computer go mailing list?

      ----

      I've forgotten what the exact SGF terminology is, but could we
      restrict the positions where this can occur so that the main line of
      play has no TP in it? That would keep it easy for "simple" programs.
      Since the full tree needs to appear somewhere, that doesn't seem
      onerous.

      cheers
      stuart

      On Tue, Jul 29, 2008 at 7:53 PM, Arno Hollosi <ahollosi@...> wrote:
      > Dear all,
      >
      > I have been approached (again) with a proposal to add links to the SGF
      > standard. As I clearly see the need for this, I would like to add it to the
      > core SGF FF[4] specification. I'd like your input on this issue before
      > finalizing the syntax.
      >
      > Here's the proposal from David Bush, author of the Twixt SGF spec:
      >
      > ""
      > TP[ simplestring ] is a node annotation property. It means this node
      > represents an identical position by TransPosition of moves to another
      > node in the tree. The value is the same as the N property of a target
      > node which must be listed earlier in the file, and must not be an
      > ancestor of the TP node. This might be useful for an opening library,
      > or anywhere that alternate move orders are plausible. A TP node should
      > be a leaf node in the file.
      >
      > Effectively, TP is like a macro call. The intention is for the software
      > to copy the subtree of the target node to the location of the TP node.
      > Strictly speaking, the two positions need not be completely identical,
      > as long as this copied subtree with all its moves, evaluations, and
      > every other property is valid in this new location.
      > ""
      >
      > comparing this with e.g. last years idea from Andre (Kogo's Dictionary)
      >
      > ""
      > Oftenly identical positions of stone result from different orders of
      > placements of these stones which are to be found in very idfferent
      > branches of joseki. In such a case, the following joseki variations are
      > included only once, and after the other order of placements a reference is
      > given. But this reference is only a description, not a hyperlink, and that
      > is unnecessarily complicated for me as author and the users and frustrated
      > to search through the branches instead of simply clicking
      > like in HTML.
      > I propose the following syntax:
      > AC[example] Anchor
      > LI[example] Link
      > The anchor is hidden to the viewer. The simplextext of the Link is
      > displayed in like that of C[] and underlined. Clicked, the sgf viewer
      > jumps to the move in the branch where the Anchor with the same simpletext is
      > attached.
      > ""
      >
      >
      > My currrent favourite option is to use N[] as the anchor, and LI[]/TP[] (we
      > have to decide on a name) as single property in a node. Also, we could think
      > about allowing links inside C[].
      >
      > I'd like to hear your opinions.
      >
      > regards,
      > /Arno
      >
      >
    • Michal Kovařík
      Hello, I support this extension vry much, but I believe that the restriction of the identical position is too restrictive, when I was making my private sgf
      Message 2 of 12 , Jul 29, 2008
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        Hello, I support this extension vry much, but I believe that the
        restriction of the identical position is too restrictive, when I was
        making my private sgf extension to solve this, I made the
        Label/Pointer tags but the pointer tag also contained information
        about transformation (axes, colors), so the dictionary joseki didn't
        need to repeat any variations with same logic.

        On Tue, Jul 29, 2008 at 10:48 AM, Stuart A. Yeates <syeates@...> wrote:
        > Great idea Anro
        >
        > Is he plan to extend sgfc to cover this and optionally expand trees?
        >
        > ----
        >
        > The idea of common subtrees is very common in computer go. I'm not
        > sure whether any of the computer go programs externalise their search
        > trees though. May I suggest that his issue is also raised on the
        > computer go mailing list?
        >
        > ----
        >
        > I've forgotten what the exact SGF terminology is, but could we
        > restrict the positions where this can occur so that the main line of
        > play has no TP in it? That would keep it easy for "simple" programs.
        > Since the full tree needs to appear somewhere, that doesn't seem
        > onerous.
        >
        > cheers
        > stuart
        >
        > On Tue, Jul 29, 2008 at 7:53 PM, Arno Hollosi <ahollosi@...> wrote:
        >> Dear all,
        >>
        >> I have been approached (again) with a proposal to add links to the SGF
        >> standard. As I clearly see the need for this, I would like to add it to
        >> the
        >> core SGF FF[4] specification. I'd like your input on this issue before
        >> finalizing the syntax.
        >>
        >> Here's the proposal from David Bush, author of the Twixt SGF spec:
        >>
        >> ""
        >> TP[ simplestring ] is a node annotation property. It means this node
        >> represents an identical position by TransPosition of moves to another
        >> node in the tree. The value is the same as the N property of a target
        >> node which must be listed earlier in the file, and must not be an
        >> ancestor of the TP node. This might be useful for an opening library,
        >> or anywhere that alternate move orders are plausible. A TP node should
        >> be a leaf node in the file.
        >>
        >> Effectively, TP is like a macro call. The intention is for the software
        >> to copy the subtree of the target node to the location of the TP node.
        >> Strictly speaking, the two positions need not be completely identical,
        >> as long as this copied subtree with all its moves, evaluations, and
        >> every other property is valid in this new location.
        >> ""
        >>
        >> comparing this with e.g. last years idea from Andre (Kogo's Dictionary)
        >>
        >> ""
        >> Oftenly identical positions of stone result from different orders of
        >> placements of these stones which are to be found in very idfferent
        >> branches of joseki. In such a case, the following joseki variations are
        >> included only once, and after the other order of placements a reference is
        >> given. But this reference is only a description, not a hyperlink, and that
        >> is unnecessarily complicated for me as author and the users and frustrated
        >> to search through the branches instead of simply clicking
        >> like in HTML.
        >> I propose the following syntax:
        >> AC[example] Anchor
        >> LI[example] Link
        >> The anchor is hidden to the viewer. The simplextext of the Link is
        >> displayed in like that of C[] and underlined. Clicked, the sgf viewer
        >> jumps to the move in the branch where the Anchor with the same simpletext
        >> is
        >> attached.
        >> ""
        >>
        >>
        >> My currrent favourite option is to use N[] as the anchor, and LI[]/TP[]
        >> (we
        >> have to decide on a name) as single property in a node. Also, we could
        >> think
        >> about allowing links inside C[].
        >>
        >> I'd like to hear your opinions.
        >>
        >> regards,
        >> /Arno
        >>
        >>
        >



        --

        Michal Kovařík
      • David Bush
        ... Duplication by reflection and/or rotation is certainly important, but this could usually be settled after the first two moves of the game. Maybe a separate
        Message 3 of 12 , Jul 29, 2008
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          > Hello, I support this extension vry much, but I believe that the
          > restriction of the identical position is too restrictive, when I was
          > making my private sgf extension to solve this, I made the
          > Label/Pointer tags but the pointer tag also contained information
          > about transformation (axes, colors), so the dictionary joseki didn't
          > need to repeat any variations with same logic.

          Duplication by reflection and/or rotation is certainly important, but
          this could usually be settled after the first two moves of the game.
          Maybe a separate property should deal with this, which is restricted
          to the beginning of the tree, maybe even in the game info node. You
          might even use an existing property such as ON. Besides naming the
          opening, the value in ON could indicate how the actual game is
          oriented compared to the moves listed in the file. The
          TP property should be allowed throughout the file, subject to two
          restrictions listed below.

          > I've forgotten what the exact SGF terminology is, but could we
          > restrict the positions where this can occur so that the main line of
          > play has no TP in it? That would keep it easy for "simple" programs.
          > Since the full tree needs to appear somewhere, that doesn't seem
          > onerous.

          Since the first variation listed is the main variation, this request
          is covered by my two restrictions:

          1. The target node must be listed before the TP node in the file.

          2. The target node must not be an ancestor of the TP node.

          This implies that the main variation cannot contain a TP property,
          because all the nodes previous to a main node are ancestors of that node.

          Regarding the issue of whether TP functions as a link or as a macro
          call, I suppose that would be up to whoever writes the software that
          uses it. The above restrictions are intended to avoid any endless loop
          of references. That's not very likely in Go, but SGF is for many games.
        • William Shubert
          ... TP is fine with me, but the requirement that it s target N[] appear before the matching TP[] is strange. Why have it? That means that if somebody reorders
          Message 4 of 12 , Jul 29, 2008
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            On Tue, 2008-07-29 at 09:53 +0200, Arno Hollosi wrote:
            TP[ simplestring ] is a node annotation property. It means this node
            represents an identical position by TransPosition of moves to another
            node in the tree. The value is the same as the N property of a target
            node which must be listed earlier in the file, and must not be an
            ancestor of the TP node. This might be useful for an opening library,
            or anywhere that alternate move orders are plausible. A TP node should
            be a leaf node in the file.
            

            TP is fine with me, but the requirement that it's target N[] appear before the matching TP[] is strange. Why have it? That means that if somebody reorders the subtrees in an SGF file, the app will need to go through the subtrees, rearranging the N[]/TP[] groups to make sure that the N comes first. Let's face it, that won't happen, so you'll end up with a lot of invalid files floating around.

            On top of that, I don't see any reason why having the N[] first makes things easier for anybody. It's not like it's easier to search the start of the file than it is to search the whole file. Sure, if you resolve the TP links as you read the file then the N must come first, but just read in the file, then resolve the links, and the problem is solved.
          • David Bush
            ... You might have missed my post from about an hour ago. It might not have reached you before you posted. The purpose of the restrictions is to avoid forward
            Message 5 of 12 , Jul 29, 2008
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              > TP is fine with me, but the requirement that it's target N[] appear
              > before the matching TP[] is strange. Why have it? That means that if
              > somebody reorders the subtrees in an SGF file, the app will need to
              > go through the subtrees, rearranging the N[]/TP[] groups to make
              > sure that the N comes first. Let's face it, that won't happen, so
              > you'll end up with a lot of invalid files floating around.

              You might have missed my post from about an hour ago. It might not
              have reached you before you posted.

              The purpose of the restrictions is to avoid forward references, which
              could result in an endless loop bug, depending on the software which
              is using the file. Software generally reads files from beginning to
              end. At the moment it encounters a forward reference, it won't be able
              to resolve that reference until it reads the target later in the file,
              so it will have to be smart enough to remember where the TP call was,
              and go back and fill in the required information after it reads the
              target. I'm trying to make it easier for programmers to incorporate TP.

              If TP is treated as a macro call, then when the file is initially
              read, a duplicate subtree or "expanded macro" will replace each TP
              call. The user could work with this enlarged tree which will not have
              any TP calls in it. Manipulating the branches should not present any
              problem.

              > On top of that, I don't see any reason why having the N[] first
              > makes things easier for anybody. It's not like it's easier to
              > search the start of the file than it is to search the whole file.
              > Sure, if you resolve the TP links as you read the file then the N
              > must come first, but just read in the file, then resolve the links,
              > and the problem is solved.

              Besides helping programmers, the two restrictions "N first" and "N
              must not be an ancestor of the TP" can create a uniform standard which
              makes it more likely that files can be used in a variety of software,
              which is what SGF is all about.

              One user asked that TP should not appear in the main line. As my
              previous post explains, these restrictions guarantee that.
            • Arno Hollosi
              ... I would certainly add such an option to SGFC. ... I tend to agree with Bill. I think that most of us agree that we should keep the SGF game tree a
              Message 6 of 12 , Jul 29, 2008
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                Stuart asked:
                > Is the plan to extend sgfc to cover this and optionally expand trees?

                I would certainly add such an option to SGFC.

                Bill wrote:
                >> TP is fine with me, but the requirement that it's target N[] appear
                >> before the matching TP[] is strange. Why have it?

                I tend to agree with Bill. I think that most of us agree that we should
                keep the SGF game tree a directed, non-cylic graph. However, as Bill
                pointed out, as soon as someone reorders variations the TP[] and subtree
                denoted by N[] would have to change place as well. That is not exactly
                easy on programmers either. Thus I side with no restriction on N[]
                appearing before TP[] in the file.

                I am undecided about keeping TP[] out of the main branch. It makes some
                sense, as SGF's tree order allows programs to ignore variations and
                still read the main line.

                Michal wrote:
                > when I was making my private sgf extension to solve this, I made the
                > Label/Pointer tags but the pointer tag also contained information
                > about transformation (axes, colors), so the dictionary joseki didn't
                > need to repeat any variations with same logic.

                I have not thought about this before, but I have no objections (but, see
                below.)


                The issue I am currently thinking about is the exact semantics of TP[]
                and its implications. If we think of it as a macro that actually
                copies/expands to the subtree denoted by N[] we "mostly" know how to
                display the result.

                But can we really copy all properties as is? E.g. if transformations are
                allowed (axes, colors) what about comments like "in the upper left
                corner" or annotation properties like GB/GW (good for black/white), just
                to name a few issues.

                Also, how does navigation behave and look like? Is it really identical
                to a file that had its TP[]-macros expanded and replaced? Or does the
                standard have to mention some special issues? (Recall the mess about
                displaying variations as siblings or children.)

                Important issue: what about editing/writing such a file? Suppose I don't
                want to write the expanded tree, but the compressed macro-version. How
                does the user control whether changing a node affects both subtrees
                (N[]'s and TP[]'s) or only one of them (if the display looks exactly the
                same)? How do I tell the SGF program to create a new TP[] or
                remove/split/copy the tree denoted by N[]. I think the GUI issues (and
                therefore the usability of this extension) are not to be underestimated.


                Your opinions?


                Apart from TP[] I really think we should have something like a real
                link, where the semantics mean jumping to another node, not copying its
                subtree. The semantics for links, the navigation, display, etc. are much
                easier for links than for macro-like TP[].

                /Arno
              • Stuart A. Yeates
                ... I m also interested in the exact semantics of TP[] with respect to ko calculations. If two subtrees have different previous board positions (as opposed to
                Message 7 of 12 , Jul 29, 2008
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                  On Wed, Jul 30, 2008 at 9:46 AM, Arno Hollosi <ahollosi@...> wrote:

                  > The issue I am currently thinking about is the exact semantics of TP[] and
                  > its implications. If we think of it as a macro that actually copies/expands
                  > to the subtree denoted by N[] we "mostly" know how to display the result.

                  I'm also interested in the exact semantics of TP[] with respect to ko
                  calculations. If two subtrees have different previous board positions
                  (as opposed to the same previous board positions in a different order)
                  their children may have different legal moves. This is mainly an issue
                  when considering the endgame rather then the opening book, of course.

                  > Important issue: what about editing/writing such a file? Suppose I don't
                  > want to write the expanded tree, but the compressed macro-version. How does
                  > the user control whether changing a node affects both subtrees (N[]'s and
                  > TP[]'s) or only one of them (if the display looks exactly the same)? How do
                  > I tell the SGF program to create a new TP[] or remove/split/copy the tree
                  > denoted by N[]. I think the GUI issues (and therefore the usability of this
                  > extension) are not to be underestimated.

                  The SGF file format has succeeded by being a file format. Specifying
                  the way a program interacts with a user should be left up the program
                  author. I hope/imagine that most programs will make the presence or
                  absence of N[]'s and TP[]'s invisible to the user.

                  cheers
                  stuart
                • Arno Hollosi
                  ... Sometimes the GUI or interaction with the user has to be addressed in the specification. That s the reason why we have a ST[] property. I am just trying to
                  Message 8 of 12 , Jul 30, 2008
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                    > The SGF file format has succeeded by being a file format. Specifying
                    > the way a program interacts with a user should be left up the program
                    > author.

                    Sometimes the GUI or interaction with the user has to be addressed in
                    the specification. That's the reason why we have a ST[] property. I am
                    just trying to find out if someone thinks there may be issues.

                    > I hope/imagine that most programs will make the presence or
                    > absence of N[]'s and TP[]'s invisible to the user.

                    I think that depends. When I am editing I'd like to know whether my
                    change is copied multiple times within the SGF tree or is a local
                    modification only. Furthermore, when I know that the subtree is copied
                    (and maybe transformed) I know that I should avoid comments like "upper
                    right corner" or "B5 should be at C17".

                    /Arno
                  • Lauri Paatero
                    Hi, I think idea is good, but there are several problems with initial proposal that need some resolution: 1. N property Property N is inteded to be
                    Message 9 of 12 , Jul 30, 2008
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                      Hi,

                      I think idea is good, but there are several problems with initial
                      proposal that need some resolution:

                      1. N property

                      Property N is inteded to be user-visible and editable name for node. So
                      duplicated exists, and preventing user from giving same node name twice
                      in file is bad solution.

                      I think it would be better to define some other property (for example
                      AC[ int ]), that could be used to reference node in all cases it is
                      machine referenced. (I have planned such id for other uses, but I would
                      prefer having single standard one.)

                      Proposal: define new invisible-to-user property AC[nro] for node, and
                      use that to reference to node.

                      2. Loops

                      I would like to say loops are not allowed, bu:

                      If we consider following chain of editing
                      1. create file which contain new properties;
                      2. edit file with editor that does not know new properties (they
                      continue to exists a long time).
                      3. Open file again with editor understanding new properties.

                      Now at step 3 we may have loops, as at step 2 there is no way new rules
                      are followed, even though editor was SGF4-compliant.
                      So I think we should not add new restrictions to what is valid file.
                      Loops will exists, and programs need to be able to deal with them.
                      Also nodes with TP might not be leaf nodes anymore.

                      So in essence new limitations would invalidate SGF4-compliance of
                      program, which is exactly what standards are supposed to prevent.

                      Proposal: No new restrictions to SGF4 file structure.

                      3. Link interpretation

                      I think we should have 2 types of links:
                      - Just jump to location, as user would have moved to location (so TP
                      does not need to be leaf)
                      - Continue with referenced subtree, as proposed here.

                      t.
                      Lauri Paatero


                      Arno Hollosi wrote:
                      >> The SGF file format has succeeded by being a file format. Specifying
                      >> the way a program interacts with a user should be left up the program
                      >> author.
                      >>
                      >
                      > Sometimes the GUI or interaction with the user has to be addressed in
                      > the specification. That's the reason why we have a ST[] property. I am
                      > just trying to find out if someone thinks there may be issues.
                      >
                      >
                      >> I hope/imagine that most programs will make the presence or
                      >> absence of N[]'s and TP[]'s invisible to the user.
                      >>
                      >
                      > I think that depends. When I am editing I'd like to know whether my
                      > change is copied multiple times within the SGF tree or is a local
                      > modification only. Furthermore, when I know that the subtree is copied
                      > (and maybe transformed) I know that I should avoid comments like "upper
                      > right corner" or "B5 should be at C17".
                      >
                      > /Arno
                      >
                      > ------------------------------------
                      >
                      > SGF spec: http://www.red-bean.com/sgf/
                      > Contact: Arno Hollosi <ahollosi@...>Yahoo! Groups Links
                      >
                      >
                      >
                      >
                      >
                    • David Bush
                      ... Not only that, but if the target node is pointed to by more than one TP, you would have to make sure N comes before all of them. ... I guess it depends on
                      Message 10 of 12 , Jul 30, 2008
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                        > Bill wrote:
                        > TP is fine with me, but the requirement that it's target N[] appear
                        > before the matching TP[] is strange. Why have it?
                        >
                        > I tend to agree with Bill. I think that most of us agree that we
                        > should keep the SGF game tree a directed, non-cylic graph. However,
                        > as Bill pointed out, as soon as someone reorders variations the
                        > TP[] and subtree denoted by N[] would have to change place as well.

                        Not only that, but if the target node is pointed to by more than one
                        TP, you would have to make sure N comes before all of them.

                        > That is not exactly easy on programmers either.

                        I guess it depends on what the program does. It wouldn't necessarily
                        be a problem if the program deals with an expanded tree instead of the
                        compressed file.

                        The purpose of TP is to make generation of a file manually with a text
                        editor a little less tedious. If you have software that can save a
                        file in SGF format from a game tree generated with a GUI, ***THERE
                        SHOULD BE NO NEED TO DEAL WITH TP.*** So as far as I can tell, the
                        problem of reordering a file is based on the assumption that this
                        reordering is done manually, with a text editor. Just out of
                        curiosity, what would be gained by doing this?

                        As was pointed out in another post, GUI issues and file loading and
                        saving issues should be regarded as independent of each other.

                        > Michal wrote:
                        > when I was making my private sgf extension to solve this, I made
                        > the Label/Pointer tags but the pointer tag also contained
                        > information about transformation (axes, colors), so the dictionary
                        > joseki didn't need to repeat any variations with same logic.

                        Sorry, I missed your point in my earlier post. But I'm not sure what
                        scope you want this extra information to apply to. Does a joseki
                        dictionary file concern itself entirely with one corner of a 19x19
                        board? Or are you talking about referring to another corner of the
                        board which was explored earlier in the same file? If the full-board
                        positions are not effectively identical by axis/color transformation,
                        there could be a problem when software tries to evaluate this
                        position. Joseki battles are of course not independent of each other.

                        Also, do you generate this dictionary with a GUI or with a text editor?

                        > ... If we think of it as a macro that actually
                        > copies/expands to the subtree denoted by N[] we "mostly" know how
                        > to display the result.
                        >
                        > But can we really copy all properties as is? E.g. if
                        > transformations are allowed (axes, colors) what about comments like
                        > "in the upper left corner" or annotation properties like GB/GW
                        > (good for black/white), just to name a few issues.

                        Whether TP is a macro call or a link, these same issues would crop up.
                        GB versus GW could be automatically taken care of. You could just
                        ignore all comments in an copied subtree, or not copy them in the
                        first place if there is any kind of axis/color change.

                        > Important issue: what about editing/writing such a file? Suppose I
                        > don't want to write the expanded tree, but the compressed macro-
                        > version. How does the user control whether changing a node affects
                        > both subtrees (N[]'s and TP[]'s) or only one of them (if the
                        > display looks exactly the same)?

                        Under what circumstances would you want to change one subtree but not
                        the other? I'm not asking about axis/color changes here. Why should
                        the user have this option to make the subtrees of the compressed file
                        different?

                        > How do I tell the SGF program to create a new TP[] or
                        > remove/split/copy the tree denoted by N[]. I think the GUI issues
                        > (and therefore the usability of this extension) are not to be
                        > underestimated.

                        Is this SGF program a text editor or a GUI? If it's a GUI which can
                        save files in SGF format, why would you want to deal with TP calls?

                        > The semantics for links, the navigation, display, etc. are much
                        > easier for links than for macro-like TP[].

                        I don't mean to require programmers to treat TP one way or the other.
                        The SGF definition should work for any way the programmer wants to use
                        it. I just used the "macro" analogy as a way of explaining what I was
                        talking about. Sorry if I wasn't clear about that.

                        syeates said:
                        > I'm also interested in the exact semantics of TP[] with respect to
                        > ko calculations. If two subtrees have different previous board
                        > positions (as opposed to the same previous board positions in a
                        > different order) their children may have different legal moves.
                        > This is mainly an issue when considering the endgame rather then
                        > the opening book, of course.

                        My proposal is that the positions need not be identical as long as
                        every move, position evaluation, and everything else that gets copied
                        or linked to is equally valid in both situations. If there are
                        "irreconcilable differences" then they should be different subtrees.
                        In a ko situation, and perhaps for the most part in Go, different
                        battles are arguably not truly independent of each other, because one
                        usually is more important than the others at any given point. So TP
                        calls might not be appropriate if the subtree in question is large.

                        Also I recommend you take a look at my LO[] proposal (in a separate
                        thread) for dealing with LOcal battles.
                      • Mark Lentczner
                        The big issue I see to resolve is the semantic of the link. I see several possibilities discussed in the thread, and I m going to try to restate the
                        Message 11 of 12 , Jul 30, 2008
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                          The big issue I see to resolve is the semantic of the link. I see
                          several possibilities discussed in the thread, and I'm going to try to
                          restate the concisely:

                          1) Identity
                          The node referenced is the identical position as the node with the
                          link. Presumably they have the same position *after* each has applied
                          any moves.

                          2) Duplicate Sub-tree
                          The nodes that follow the referenced node are equally applicable to
                          the position at this node.

                          3) Jump
                          The referenced node should be offered to the user as a possible follow
                          on to this node. The position at the referenced node could be wholly
                          different.

                          Identity seems to have a number difficulties in definition and
                          resiliency:
                          - just how "identical" do the positions have to be?
                          - i.e.: same number of prisoners? or just same delta? passes?
                          - same comments? markup?
                          - what about differing in only a tenuki move?

                          Duplicate Sub-tree has the downside that now each node can no longer
                          be transformed into a single game position, since the state of the
                          game will depend on if you took a jump to get there.

                          Jump gets around these difficulties, but at the expense of being a
                          different kind of navigation that the existing options.

                          One way to approach the choice is to look at the use cases and see
                          which admits the most flexibility. The use cases I see are:

                          A) Joseki dictionary desire to not replicate whole sub-trees when a
                          position can be arrived at via two different move sequences. This use
                          case could be broadened to include color and spacial transposition, or
                          differing in tenuki.

                          B) Tsumego. Like joseki, a desire to not replicate whole sub-trees.
                          Here the game state identity requirement might be more rigorous.
                          GoProblems.com already does this automatically by identifying
                          identical positions in the tree: If one has follow on nodes and the
                          other doesn't -- they are "spliced".

                          C) General annotation need to have variant lines or main lines
                          reference other lines within the tree.

                          It seems to me that the Jump semantic supports all of these. If there
                          is a need for identical position at both ends, it is easy enough for
                          the creation tool to enforce that.

                          The only thing that then needs to be addressed is the intended user
                          navigation: Is it displayed as an option? Is it followed
                          automatically? One could support both by this rule: If the LI[]/TP[]
                          property appears as the only property in a node, then the link should
                          be immediately followed, replacing the game state with the state at
                          the target node. On the other hand, if there are any other
                          properties, including just a comment (even an empty comment!), then
                          the user is offered link as a sort of 'remote variation', and can
                          choose, as they would choose a variant, to continue in that part of
                          the tree.

                          - Mark
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