[elephant-devel] Query System

Wed May 14 19:20:47 UTC 2008

Daniel,

I'm just a hanger on who is trying to figure out this wonderful new world of
Lisp and Elephant. I love the discussions on this list. Elephant does things
I've always been interested in but never knew anything about. The
discussions in this group are very helpful.

Lisp makes me feel mentally challenged (well... more so than my usually
state :-) ).

Glenn

-----Original Message-----
From: elephant-devel-bounces at common-lisp.net
[mailto:elephant-devel-bounces at common-lisp.net] On Behalf Of
lists at infoway.net
Sent: Wednesday, May 14, 2008 3:07 PM
To: Elephant bugs and development
Subject: Re: [elephant-devel] Query System

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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>> elephant-devel at common-lisp.net
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>
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