Hi Andy, Hope you're well - nice to hear from you. (responses inline)
On Sat, 22 Jan 2022 at 13:57, Andy Seaborne <[email protected]> wrote: > > > > On 21/01/2022 15:26, Martynas Jusevičius wrote: > > WebAccessControl ontology might be relevant here: > > https://www.w3.org/wiki/WebAccessControl > > We're using a request filter that controls access against > > authorizations using SPARQL. > > > > > On Fri, Jan 21, 2022 at 4:13 PM Vilnis Termanis > > <[email protected]> wrote: > >> > >> Hi, > > Hi Vilnis, > > >> For a SPARQL query via Fuseki, we are trying to restrict visibility of > >> groups of triples (each with multiple subjects) dynamically, in order > >> to allow for generic queries to be executed by users (instead of > >> providing tinned ones). > > >> Looking at the available ACL mechanisms in Jena/Fuseki, I assume > >> storing each of these groups as a distinct graph might be the way > >> forward. (The expectation is to be able to support 10^5 or higher > >> number of these.) > > If each graph is in the same TDB dataset, graph numbers are not much > different from any other node frequency. Millions of graphs are > possible. It's all quads. 4 Node/NodeIds. Great, that's what I was hoping. > > So it might be a way forward (details matter...) > > Managing said dataset is another matter. > > The description sounds a bit SOLID-like - see Martynas's comment > and -> https://inrupt.com. > > >> I.e.: Given a user (external to Fuseki, e.g. presented via shiro via > >> LDAP/other), only consider triples from the set of graphs 1..N during > >> the query. (Where the allowed list of 1..N graphs is to be looked up > >> at the point of the query.) > > How often is LDAP being accessed per query execution? Going off machine > is a significant cost compared to triple access. (From experience of > others, LDAP servers can be "unhelpful" - e.g. big spread in the latency > of requests based on environmental factors). I think I could have worded that better: Given a provided (at query time) user/Principal (which Fuseki/Jena does not have to authenticate), only consider graphs 1..N (determined based on the principle.) > (shiro is only integrated for Fuseki/webapp - it does work with > Fuseki/main but you have to add it. Current WIP should, eventually, > improve this.) > > >> From my limited understanding, some potential routes are: > >> > >> a) jena-fuseki-access - Filters triples at storage level via "TDB Quad > >> Filter" support in TDB. > > Yes. Filtering is a hook to use. Sounds like your UC might need its own > filter code (in Java) for the policy. > > >> However, the configuration of allowed graphs per user is static at runtime. > > jena-fuseki-access is a layer on top of the filtering mechanism for the > common case of ACLs on named graphs. That layer isn't compulsory for > quad filtering. The code may be inspiration for setup of custom code. >From your perspective, if the UC is indeed only about graph-level filtering (and not more granular), are there specific pros/cons of implementing such a filter using the TDB quad hook VS query engine op rewriting? Is the former more efficient (due to being lower-level maybe?) or do they both in the end have a very similar job - exclude matched quads if their graphs are no in the allowed list. > > >> b) jena-permissions - Extends the SPARQL query engine with an Op > >> rewriter which allows a user-defined evalulator implementation to > >> allow/deny access to a graph/triple, given a specific user/principle. > >> (The specific yes/no evaluation responses are cached for the duration > >> of a query/operation.) > > From what I know, should work. Claude may be able to say more. > > >> However, this can only applied to a single graph as it stands. > > A dataset is a collection of named graphs. Each graph can have > jena-permissions wrapped around it. Indeed - what I wasn't sure about is how that wrapping would work in the "any-number-of-graphs" (as opposed to fixed via config) case so assumed there might be some extra work to move it up a level, to dataset. (I found a thread from 2018 where it's suggested this: https://markmail.org/message/z5tsgblnqivpdqvy ) > > Your UC description was about groups of triples, and then it slid into > named graph. Is NG points above and below about implementation > possibility or is the incoming data already using named graphs? > I only wrote "groups of triples" because I wanted to make sure that representing them each in their own graph was a sensible thing to do. You're right - my thoughts on how it could be solved were all about NGs. The data isn't currently segregated into many graphs, but it'd be relatively trivial to change this in our UC, so for my questions in this thread we can assume they are already each in their own NG. What I forgot to mention was that, in the case of (a) or (b) from above, I am imagining the querying would happen against the union graph such that clients don't need to know what the graphs are which they are allowed to see. (Hence attempt (c) using FROM rather than FROM NAMED.) > This approach will not be using the low level filtering but it may > not show. What matters is the number of visible graphs, not the total > number. Ah right - so I presume you're eluding to the fact that the TDB1/2 quad filter is a lower-level tool than the query op rewrite. Regarding your note on visible graphs - is that an implication about performance impact for both (a) & (b) when a large percentage of graphs is visible, or have I misinterpreted your statement? > Can be possibly combined with (C). Interesting - I hadn't though of that. But I'm not 100% clear on how the responsibilities might be split between (a)/(b) and (c) for this. > >> c) Parse & re-write the query to e.g. scope it using a fixed set of > >> "FROM" clauses. From some minimal testing (with ~200 FROM clauses) > >> this does not appear to perform well (compare to a tinned query which > >> explicitly restricts access via knowledge of the ontologies involved). > >> I appreciate that maybe having a large list of FROM clauses is an > >> anti-pattern. > > Quite likely - depends on the query complexity and numbers. There's a > hook in Fuseki query evaluation for this - did you try that or did you > do it client-side? I've only tried it directly in the client. I presume this hook you mention would have roughly the same perf as specifying in at the client end? > If the query is a small amount of work, the setup overhead will be > significant but it is (roughly) a fixed overhead so a longer running > query is less impacted. > > >> My questions are: > >> > >> 1) Does filtering to a set of subset of graphs (from a large set of > >> graphs) to restrict access sounds like a sensible thing to do? (Note > >> that each of these graphs would contain a set of multiple subjects - > >> i.e. we are not trying filter by specific predicate/object values.) > > Sounds possible - "sensible" depends on the details of the intended usage. > > >> 2) Would extending either jena-fuseki-access to support the > >> user-graph-list lookup dynamically OR extend jena-permissions to work > >> at dataset level be sensible things to do? > > Functionally - yes, but lots of details matter. > > And user-graph-list sounds SOLID-like. > > In the SOLID approach the access path is known and its the path that > decides access or not. Very different to filtering. Our ACL definitions (for the "this user can read these graphs") are similar to SOLID's WACL draft spec (in that, when we have more time, we should migrate to using it). I.e. we can answer the "Can user X see resource/graph Y" question using SPARQL - and we use this for tinned/parameterised queries. However, if we want to allow end-users to write their own queries but ensure the ACL still applies, then rewriting the query (using approaches other than (c)) seems complex. Although an implementation (e.g. Jena/Fuseki) independent generic SPARQL solution would be great - we're considering all approaches for performance reasons. > >> 3) If the answer to either of (2) is yes - I'd be interested in > >> getting a better understanding of what would be involved to gauge the > >> size/effort of such an extension. I have had a look codebases for the > >> aforementioned projects, but my knowledge of TDB/ARQ/etc is very > >> limited. (We'd potentially be interested in taking this on, time & > >> priorities permitting.) > > Great! > > >> I didn't know which mailing list to send this to but I thought the > >> users list would probably be a better starting point. > > Here is OK. > > Andy > > >> > >> Regards, > >> Vilnis > >> > >> -- > >> Vilnis Termanis > >> Senior Software Developer > >> > >> e | [email protected] > >> www.iotics.com -- Vilnis Termanis Senior Software Developer e | [email protected] www.iotics.com
