[elephant-devel] Query System

[lists at infoway.net]

Ian/Glenn,

Thanks for the feedback. I knew it should be somewhere buried within  
the MOP and last week I ordered The Art of the MOP but am waiting for  
it to arrive. I also know it will take me some time to grasp it. I  
just wanted to get some familiarity for this particular need (more  
specifically, I was thinking of allowing the query to ask for things  
like Person.name or something like that, but wanted to know if it was  
possible to "pre-compile" the query and make sure that the name slot  
exists on the Person class; BTW, sorry for my non-Lisp syntax).

Anyway, I am reading OnLisp. Definitely impressed and perplexed as to  
what can be done with macros, but I'm getting it slowly :)

I hope to be able to submit a draft proposal by tomorrow. Maybe I'll  
send to you privately for review and comment before posting it to the  
list - and possibly ridicule myself :)

Anyway, will look into your suggestions right away.

Thanks,
Daniel

On May 14, 2008, at 2:25 PM, V. Glenn Tarcea wrote:

>
> Some great books and PDFs:
>
> The Art of the Meta Object Protocol (available on Amazon)
> Object-Oriented Programming in COMMON LISP (Keene, also on Amazon)
>
> For Advance mind twisting Lisp, get Paul Graham's OnLisp (available  
> as a
> downloadable PDF). My brain hurts just trying to figure out some of  
> the
> macros (and even more advance features) he rolls out:
> http://www.paulgraham.com/onlisptext.html
>
> I would have to say that "The Art of the Meta Object Protocol" is  
> one of the
> best comp sci books in my collection.
>
> Glenn
>
> -----Original Message-----
> From: elephant-devel-bounces at common-lisp.net
> [mailto:elephant-devel-bounces at common-lisp.net] On Behalf Of Ian  
> Eslick
> Sent: Wednesday, May 14, 2008 2:16 PM
> To: Elephant bugs and development
> Subject: Re: [elephant-devel] Query System
>
> Hi Daniel,
>
> Welcome to the Metaobject Protocol, aka the MOP!  There is a rich
> embedded language for introspecting over and manipulating the class
> system in lisp that Elephant uses heavily.  You could have a procedure
> extract the and caches the essential information from the class slot
> definitions into a little structure.  You can do this the first time
> the query system encounters a class, and add a hook into the class
> instantiation code that invalidates the cache on class redefinition.
> It's worth diving into it, but it can take awhile to wrap your head
> around the concepts, not to mention the idiosyncrasies of the MOP.
>
> I'm happy to review your proposal offline or online as you prefer.
>
> If you look at src/elephant/package.lisp we import symbols selectively
> from the metaobject protocol package specific to each lisp.  The
> functions you are looking for are:
>
> class-slots - return a list of slot-definition-objects
>
> Each of the special elephant slots returned by this function is a
> subtype of the class standard-effective-slot-definition and  
> persistent-
> effective-slot-definition.  Direct slots are representations of the
> arguments to the defclass form.  Effective slots are computed when the
> class is 'finalized' (i.e. the first instance is instantiated and it's
> inheritance hierarchy is fully defined).  A generic function called
> slot-definition-using-class dispatches on the type of the effective
> slot to implement the common-lisp primitive (slot-value obj slotname)
>
> The special types you'll care about are:
> - persistent-effective-slot-definition
>   persistent-p is a predicate on the slot definition that tells you
> if it is an instance of or subclass of a persistent slot.
> - indexed-effective-slot-definition
>   (has special slots named: indices and base-class; predicate is
> indexed-p)
> - derived-effective-slot-definition
>   (derived from the index slot also contains a slot: fn for
> determining the value to index on)
> - set-valued-effective-slot-definition
>   (slot stores a reference to a pset; set-valued-p)
> - association-effective-slot-definition
>   (association-p; this is complicated so we should handle this as a
> special case in the query system later)
>
> I have accessors to get these slots from the class object such as
> association-slot-defs, indexed-slot-defs, and persistent-slot-defs.
>
> Read metaclasses.lisp for more information on these definitions.
>
> If you know an index exists on a class slot, you can simply call  
> (find-
> inverted-index class-object slotname) to have the system fetch it for
> you.
>
> This should be enough for you to define a structure like:
>
> (defstruct class-info classname slotypes)
>
> Where slottypes is an alist:
> - ((slotname . :indexed) (slotname . :persistent)
> (slotname . :transient))
>
> or something like that.
>
> Ian
>
> On May 14, 2008, at 1:45 PM, lists at infoway.net wrote:
>
>> I've digested Ian and Leslie's comments on this thread and think
>> we're all on the same page now. I've been reading different papers
>> and other OODBMs in trying to propose a querying syntax and am
>> pretty close to completing this now. However, I have some doubts for
>> which I'll need someone's help with, which will allow me to continue
>> drafting my proposal.
>>
>> I believe Ian (if it was someone else, I apologize for not quoting
>> you) mentioned that we could, as a later phase, introspect the class
>> and ask for the indices available in order to do some query
>> optimizations. So my question goes somewhere along those lines and
>> I'm wondering (please excuse my limited knowledge of Lisp and thank
>> you for helping my learning curve) if it's possible to obtain the
>> list of slots and/or slot-accessor functions for a given class.
>>
>> Thanks,
>> Daniel
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