Skewer, Pin and X-Ray Attack

[alvarofrota]

Prezados ChessTempistas:

The tactical motif of problem number 45903 is a X-Ray Attack, a Skewer or a Pin?

After 1. ... Rb8-d8 the solution is 2. Dd7-h3, reaching the position:



It looks like a Skewer: Blakc Queen must move. But, if the Queen moves, White mates at "h7", then, it is not a Skewer but an Absolute Pin.

Anyway, it is not a X-Ray Attack.

IMO.

What are your opinion?

Aquele abraço!

[aras]

These terms are not absolute so X-ray is a kind of skewer and a skewer is sort of like apin.  This can be seen as an X-ray as the rook is attacking the king through the pawn and the queen.

[phdevos]

I would say pin. h7 is more important than the queen in this position, because it's mate. Without the bishop on c4 (so Rxh7 wouldn't be mate) I would call it a skewer.

About the X-ray/skewer, see this thread too: http://chesstempo.com/chess-forum/tactics_problems/skewer_xray-t1478.0.html

[richard]

I also think this is a pin, if it was a skewer the queen would move away and whatever was behind would fall, but here (as phdevos points out) , what is behind the queen is actually more important than the queen, so the queen is pinned.

I find x-ray confusing, so I'll leave others to comment on that aspect :-)

Richard.

[alvarofrota]

Surely there is a X-Ray Attack in the above position. White battery Rock + Queen do is attacking "h7" through the Black Queen. But this motif is meaningless because there is nothing that White can do to utilze it.

If the other White Rock was at the 7º rank, the X-Ray motif would be the more important one but, as this is not happening, the problem do not be tagged as X-Ray Attack.

IMO

[phdevos]

Exactly what I thought!

I think the tag description for X-ray could do with a rephrasing. It should mention something about a second piece capturing the last piece. I think Drahacikfm phrased the point very well in another thread:

An X-ray attack is that it always involves two White pieces (assuming White is the one doing the attacking).  The two White pieces are attacking a piece or square in Black's camp: one White piece is attacking directly, and the other White piece is attacking through another Black piece.

On the other hand, a skewer involves only one White piece.

[richard]

Hi phdevos,

There are a couple of tag descriptions I'd like to tweak, I'll probably do this next time I add new tags (still a few weeks away unfortunately).

Regards,
Richard.

[alvarofrota]

Prezado Richard:

Despite the schedule and the contents of the site's modifications is (of course) up to you, I think it will be great if we start in this Forum some discussions about the new Tags and about the descriptions of all Tags.

Someone have a list of all the propositions made here?

Aquele abraço!

[drahacikfm]

Some detailed discussions of tags, their descriptions, and proposed new tags already exists in the Forum.  You can look for them in the Chess Tactics Discussion section and add any new comments you have there.

[alvarofrota]

Thank you very much, Drahacikfm!

[roq]

Some chess authors use the term X-ray when a piece threatens an opposing piece through a friendly piece, so that for instance a white rook on e1 might be said to be x-raying a queen on e8 through a white pawn on e4. IMOP the term X-ray can be used for any situation where one piece is threatening another through a blocking piece. In that case all pins and skewers are also x-rays. Should be removed as a tag IMOP, since it's usage is too ambiguos.

I noticed one problem where a rook was pinning (?) a knight with the other knight being the blocking piece. The first comment said: Couldn't be a pin, since the blocking piece was not less valuable than the blocked piece and couldn't be a skewer for the opposite reason so must be an x-ray!    

     

[richard]

Hi roq,

I disagree, just because a tag is used ambiguously in the literature doesn't mean it can't be defined un-ambiguously here.  The most common ambiguity I've seen with x-ray is that some authors use it interchangeably with skewer, although in English language chess literature, the definition used on CT still seems to be the most common usage, and the one higher rated players on here seem to most commonly use when they think of x-ray attacks (at least the native English speaking ones). From what I can see your definition can be found in the literature, but is a minority opinion, and in any case clashes with the CT 'ignore everything else you've heard, this is how CT defines this tag' definition :-)

Regards,
Richard.

[phdevos]

Roq's example sounds really a lot like what I came across when I tried to figure it all out to be able to translate those tags. Wikipedia uses 3 different meanings for X-ray:

"In chess, the term X-ray or X-ray attack is sometimes used (1) as a synonym for skewer. The term is also sometimes used to refer to a tactic where a piece either (2) indirectly attacks an enemy piece through another piece or pieces or (3) defends a friendly piece through an enemy piece."

If I am not mistaken, on CT it's not really any of the 3, or just a specific case of meaning (2), which may result in a position that could be described by (3). In my humble opinion, the value of the pieces only makes it more confusing (it's true that the relative value of the pieces is irrelevant though).

Anyway, I don't think that the tag is ambiguous, but the Chess Tempo definition could be more precise. As Richard has pointed out in this threat, that's on the list, and I think for now the description is sufficient (no matter how you define it, there will always be room for discussion). If we'd throw out all the tags that are used for different motifs in literature, there's a whole bunch of them that could be deleted (attraction, distraction, sacrifice, hanging piece, exposed king, blocking, clearance, etc.).


I think that if people would actually read those descriptions before they start their click-fest, we wouldn't even be having this discussion in the first place...

[richard]

I agree that ambiguity in the literature isn't enough, if the situation is interesting (and common) enough then I think we should try and have a tag for it, even if that requires a more precise definition than is usually used.

I agree that there are a few tags which could do with some more precise (or perhaps just clearer) descriptions, X-Ray amongst them, but I also agree that the main problem is probably those who do not read or do not understand the descriptions, a little better wording of the descriptions and the translations should help with the later case.  I've also considered forcing the users to have at least visited the tag descriptions page before being able to vote on tags, but I think most users that were going to ignore the descriptions anyway, will still continue to do so, even if they are forced to visit the descriptions page.

Ultimately I think weighting user votes will be a big help, not only will this improve the quality of the final outcome, but it can also be used to show per-tag feedback to users on which tags they are making that other people disagree with regularly (with a link to the tag description page which they might now actually read after being shown negative feedback on their voting patterns).

Regards,
Richard.

[drahacikfm]

I think that if people would actually read those descriptions before they start their click-fest, we wouldn't even be having this discussion in the first place...

Yes!  Of course they don't read the Forum either.

Richard, I know it's not a high priority, but ideally there should be a tagging test for new users.  10 problems or so, carefully chosen so the tags are clear and not controversial.  People need to tag 9 out of 10 correctly before they can tag real problems.

But maybe the weighting system will take care of that well enough.

On a recent problem I wrote a comment that problems can't have Back Rank Mate and Weak Back Rank tags at the same time.  A user argued that in his opinion it could.  I replied that if you read the tag description page and follow those definitions it's not a matter of opinion.  If the mate occurs, it's Back Rank Mate.  If you win material because of threats of a mate, it's Weak Back Rank.  To put both is wrong.

The point is CT has specific definitions which might differ from other sources such as Wikipedia or chess books, but the CT definitions should be followed when tagging.