Markus:
This is certainly an interesting development, but now I need to know:
Where does that leave a wiki administrator, like myself, who created a
multitude of properties of Type:Page, and their inverses, and even
developed template code to mark up a page with inverse-property
annotations to point right back to every page that pointed to the page
in question? For example: in an article describing, say, the planet
Saturn, I included this instruction: "Annotate this page multiple times
with the property of "Satellite," the values of which shall be the names
of every page that listed this page as "Primary." In that manner, Saturn
is automatically annotated with [[Satellite::Mimas]],
[[Satellite::Enceladus]], /et cetera/, because the articles on Mimas and
Enceladus list Saturn as their primary.
Now you tell me that, beginning with the next snapshot release of SMW,
much of that markup will be unnecessary.
In other words, if I wanted to find all the capital cities of a given
region, I would need to:
{{#ask:[[-Capital.region::Middle East]] }}
and I would get Jerusalem, Amman, Damascus, Cairo, Baghdad, Beirut,
Doha, and Kuwait City, so long as I had annotated the articles on
Israel, Jordan, Syria, Egypt, Iraq, Qatar, and Kuwait with a value for
the property called "Capital." Thus I would not need to annotate
Jerusalem with the notation [[Is capital of::Israel]].
So tell me this: Would I ever need to make an explicit declaration of an
inverse property?
Under what circumstances would such inverse declaration be valuable? I
can think of one: genealogical references. Specifically: the property
"Father of" could have not just one inverse, but two: "Son of" and
"Daughter of." Likewise, either "Son of" or "daughter of" has a
non-exclusive inverse relationship with the properties "Father of" and
"Mother of." Now if I had simply declared "Parent of" and "Child of,"
then the inverse relationships would be one-to-one and I could simply
declare one or the other, and not both.
Well, it looks as though I'll have a lot of cleanup to do. Clearly, a
lot of those inverse properties will no longer be necessary.
Question: Does SMW have a tool to find out which properties are
currently referred to in a query or concept? I wouldn't want to
"undeclare" or "deannotate" a property if it's going to break a query.
Temlakos
Markus Krötzsch wrote:
> Using the Codeathon at Wikimania 2009, we have now implemented support for
> "inverse properties". This email gives an overview of the features (usr
> perspective) and internals (developer perspectives). Some SMW extensions will
> need to be adjusted to work with the new feature.
>
> == Introduction ==
>
> The inverse of a property simply is the property that points into the other
> direction. For example, if "developer of" connects a person to a software
> tool, then the inverse of "developer of" connects software tools to persons.
> So far, it was very hard to use properties in other directions. In our
> example, you could, e.g., have an ask query showing the all persons who
> develop some open source tool, but you could not have a query that shows all
> software tools that are developed by people living in Argentina. To do the
> latter, you would have had to use a property "is developed by" that
> explicitly
> connects software tools to their developers, and you would have had to add
> data for that again. If you need both directions, you would have to maintain
> both properties individually, which is not very convenient.
>
> == Feature Details ==
>
> SMW (SVN) now allows you to directly refer to the inverse of any property by
> simply putting a "-" in front of its name. For example, "-developer of" gives
> you access to what I called "is developed by" above. This can be used in any
> place where property names occur, including browsing special pages, ask
> queries, and output directives of queries. So the projects developed by
> people
> from Argentina can be obtained with a query
>
> {{#ask: [[-developer of:: <q>[[lives in::Argentina]]</q> ]] }}
>
> or simply
>
> {{#ask: [[-developer of.lives in::Argentina]] }}
>
>
> We are aware that the "-" prefix is not the most readable way of solving the
> problem. However, the solution we have now avoids a number of complications
> that other solution would introduce (for example, you cannot have chains of
> inverses, like Property:A inverse_of Property:B inverse_of Property:C
> inverse_of ...; also, there is no relevant interplay of "subproperty of" and
> inverses).
>
> If applicable, inverse properties generally are linked to the page of the
> corresponding property (so "-developer of" links to "Property:developer of").
> It is strongly suggested not to create property pages that are called like
> inverse properties (it won't destroy anything, but it might create
> unnecessary
> confusion). Also, you cannot use inverse properties to enter semantic data
> into the wiki: all annotations must be on the page that is the subject of the
> non-inverted property.
>
> Inverses in queries are currently only supported if they are of Type:Page.
>
>
> == Development Information ==
>
> If your code uses SMW properties that are generated from user inputs, then
> you
> need to be aware of inverse properties to make sure everything works
> correctly. Internally, an inverse property, like any property, is represented
> by an SMWPropertyValue object. It will look like the property value object
> for
> the non-inverse version of the property. To check if it actually is the
> inverse, you can use the new method isInverse(). You can pass inverse
> properties to the SMW store, and it will take care of everything.
>
> The main changes that I expect to be required in SMW extensions is in places
> where you deal with property subjects and silently expect them to be of
> Type:Page. If users can enter inverse properties, then a query for a subject
> can also return datavalues of other datatypes, so you need to use the generic
> datavalue API, or check the type of the datavalue first.
>
> Another place where changes might be needed is when passing on parameters as
> strings. If you use getWikiValue() on an inverse property, then you will
> obtain the property name with "-" in front, as expected. But if you use
> "getShortWiikiText()" and other functions, you will get the name of the
> property without any "-".
>
>
> I hope that SMW already works properly in all cases where inverses can occur.
> Feedback is welcome.
>
> Cheers,
>
> Markus
>
>
> ------------------------------------------------------------------------
>
> ------------------------------------------------------------------------------
> Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day
> trial. Simplify your report design, integration and deployment - and focus on
> what you do best, core application coding. Discover what's new with
> Crystal Reports now. http://p.sf.net/sfu/bobj-july
> ------------------------------------------------------------------------
>
> _______________________________________________
> Semediawiki-devel mailing list
> Semediawiki-devel@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/semediawiki-devel
>
------------------------------------------------------------------------------
Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day
trial. Simplify your report design, integration and deployment - and focus on
what you do best, core application coding. Discover what's new with
Crystal Reports now. http://p.sf.net/sfu/bobj-july
_______________________________________________
Semediawiki-devel mailing list
Semediawiki-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/semediawiki-devel
