Re: Why are RDF containers (rdf:Seq etc.) so little appreciated?
Im not sure what you mean by 'stable identity', It's a slightly (possibly unorthodox) viewpoint I take during RDF editing: With a container, you can say I will edit the sequence at URI X and be sure that X stays the same, no matter how you change the elements. With a collection, the anchor changes whenever one goes from 0 elements to 1 or more elements (or vice versa). Giving a collection a stable identity seems to have been one of the motivations behind skos:OrderedCollection. but the chief problem with containers is the fact that there is no way to 'close' them. If I say that FOO is a container and A, B and C are in it, there is no way to say that this is *all* that is in it. This makes them useless for encoding structures, eg OWL syntax. Collections' overcome this difficulty. So the collection notion is widely used to layer higher-level notations onto RDF, which is probably why toolkits have special provision for them. I see the point, but it seems like one could achieve the same effect by adding an additional nil element (at the end) to a container. This does not stop you using the containers, of course. They are simple enough that you hardly need syntactic sugar, right? True. -- axel.rauschma...@ifi.lmu.de http://www.pst.ifi.lmu.de/~rauschma/
Re: Why are RDF containers (rdf:Seq etc.) so little appreciated?
On Feb 14, 2010, at 4:34 AM, Axel Rauschmayer wrote: Im not sure what you mean by 'stable identity', It's a slightly (possibly unorthodox) viewpoint I take during RDF editing: With a container, you can say I will edit the sequence at URI X and be sure that X stays the same, no matter how you change the elements. With a collection, the anchor changes whenever one goes from 0 elements to 1 or more elements (or vice versa). Giving a collection a stable identity seems to have been one of the motivations behind skos:OrderedCollection. Ah, I see. Ironically, this is the source of the problem. but the chief problem with containers is the fact that there is no way to 'close' them. If I say that FOO is a container and A, B and C are in it, there is no way to say that this is *all* that is in it. This makes them useless for encoding structures, eg OWL syntax. Collections' overcome this difficulty. So the collection notion is widely used to layer higher-level notations onto RDF, which is probably why toolkits have special provision for them. I see the point, but it seems like one could achieve the same effect by adding an additional nil element (at the end) to a container. No, you can't. The problem is that this would (if it were effective) make the logic nonmonotonic. Put another way, objects described in RDF cannot have 'state' in the computational sense. They cannot 'change' by adding new assertions. Whatever was true before you say the new stuff has to stay true afterwards. So you can't take a container and *change* the elements it has, eg go from 0 to 1 elements, by adding assertions. The great advantage of lists is, when you add an element to a list, you are in fact creating a new list: the old list is still around and is still what it was before the addition. This is why lists (collections) work in RDF, more or less, while containers don't. That is, RDF containers, so called, are not really containers in the usual sense one would think of when talking about data structures. This is also why lists don't have what you call a stable identity: what you want is the longer list after the addition to be the *same list* with a changed state, but that isn't possible in RDF because there is no state to change. Pat This does not stop you using the containers, of course. They are simple enough that you hardly need syntactic sugar, right? True. -- axel.rauschma...@ifi.lmu.de http://www.pst.ifi.lmu.de/~rauschma/ IHMC (850)434 8903 or (650)494 3973 40 South Alcaniz St. (850)202 4416 office Pensacola(850)202 4440 fax FL 32502 (850)291 0667 mobile phayesAT-SIGNihmc.us http://www.ihmc.us/users/phayes
Re: Why are RDF containers (rdf:Seq etc.) so little appreciated?
On 2/14/10 5:58 PM, Pat Hayes wrote: On Feb 14, 2010, at 4:34 AM, Axel Rauschmayer wrote: Im not sure what you mean by 'stable identity', It's a slightly (possibly unorthodox) viewpoint I take during RDF editing: With a container, you can say I will edit the sequence at URI X and be sure that X stays the same, no matter how you change the elements. With a collection, the anchor changes whenever one goes from 0 elements to 1 or more elements (or vice versa). Giving a collection a stable identity seems to have been one of the motivations behind skos:OrderedCollection. Ah, I see. Ironically, this is the source of the problem. I'm not really sure that Giving a collection a stable identity was the motivation for skos:OrderedCollection. As a matter of fact, I don't see why a List should always have a less stable identity than a SKOS ordered collection... Antoine but the chief problem with containers is the fact that there is no way to 'close' them. If I say that FOO is a container and A, B and C are in it, there is no way to say that this is *all* that is in it. This makes them useless for encoding structures, eg OWL syntax. Collections' overcome this difficulty. So the collection notion is widely used to layer higher-level notations onto RDF, which is probably why toolkits have special provision for them. I see the point, but it seems like one could achieve the same effect by adding an additional nil element (at the end) to a container. No, you can't. The problem is that this would (if it were effective) make the logic nonmonotonic. Put another way, objects described in RDF cannot have 'state' in the computational sense. They cannot 'change' by adding new assertions. Whatever was true before you say the new stuff has to stay true afterwards. So you can't take a container and *change* the elements it has, eg go from 0 to 1 elements, by adding assertions. The great advantage of lists is, when you add an element to a list, you are in fact creating a new list: the old list is still around and is still what it was before the addition. This is why lists (collections) work in RDF, more or less, while containers don't. That is, RDF containers, so called, are not really containers in the usual sense one would think of when talking about data structures. This is also why lists don't have what you call a stable identity: what you want is the longer list after the addition to be the *same list* with a changed state, but that isn't possible in RDF because there is no state to change. Pat This does not stop you using the containers, of course. They are simple enough that you hardly need syntactic sugar, right? True. -- axel.rauschma...@ifi.lmu.de http://www.pst.ifi.lmu.de/~rauschma/ IHMC (850)434 8903 or (650)494 3973 40 South Alcaniz St. (850)202 4416 office Pensacola (850)202 4440 fax FL 32502 (850)291 0667 mobile phayesAT-SIGNihmc.us http://www.ihmc.us/users/phayes
Why are RDF containers (rdf:Seq etc.) so little appreciated?
In contrast to RDF collections (rdf:List), they have a stable identity and don't use nested resources (=easy to remove). Furthermore, standard RDFS inferencing can be used to infer membership as the property rdfs:member. Yet, most RDF vocabularies that I know of use collections and syntaxes such as Turtle have syntactic sugar for collections, but not for containers. Why is that? Axel -- axel.rauschma...@ifi.lmu.de http://www.pst.ifi.lmu.de/~rauschma/
Re: Why are RDF containers (rdf:Seq etc.) so little appreciated?
Im not sure what you mean by 'stable identity', but the chief problem with containers is the fact that there is no way to 'close' them. If I say that FOO is a container and A, B and C are in it, there is no way to say that this is *all* that is in it. This makes them useless for encoding structures, eg OWL syntax. Collections' overcome this difficulty. So the collection notion is widely used to layer higher- level notations onto RDF, which is probably why toolkits have special provision for them. This does not stop you using the containers, of course. They are simple enough that you hardly need syntactic sugar, right? Pat Hayes On Feb 13, 2010, at 8:28 AM, Axel Rauschmayer wrote: In contrast to RDF collections (rdf:List), they have a stable identity and don't use nested resources (=easy to remove). Furthermore, standard RDFS inferencing can be used to infer membership as the property rdfs:member. Yet, most RDF vocabularies that I know of use collections and syntaxes such as Turtle have syntactic sugar for collections, but not for containers. Why is that? Axel -- axel.rauschma...@ifi.lmu.de http://www.pst.ifi.lmu.de/~rauschma/ IHMC (850)434 8903 or (650)494 3973 40 South Alcaniz St. (850)202 4416 office Pensacola(850)202 4440 fax FL 32502 (850)291 0667 mobile phayesAT-SIGNihmc.us http://www.ihmc.us/users/phayes
