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Repost: Questions regarding the Ent
- To: udanax@xxxxxxxxxx
- Subject: Repost: Questions regarding the Ent
- From: Jeff Rush <jrush@xxxxxxxxxx>
- Date: Wed, 30 Jan 2002 10:34:33 -0600
- Sender: jrush@xxxxxxxxxxxxxx
Mark S Miller wrote:
> At 06:18 AM 1/25/2002 Friday, Jeff Rush wrote:
> >1. what kind of enfilade is an OTree? They look like they might
> > be type 1 (DSP only, no WID). Are type 2 enfilades used
> > _anywhere_ in Gold?
> On the way from Green to Gold, Wids got replaced with Splits. Similar in
> concept, but Splits scale much better. We got the idea by trying to imagine
> how Enfilades relate to K-D-Trees.
> Can you give us a pointer on type1 vs type2 enfilades? I don't remember
> this classification.
> >2. canopies are implemented as AVL trees, correct?
> I don't remember thinking of them as AVL trees, but I also don't remember
> what kind of balancing properties they had.
> >The bert
> > and recorder canopies are _identical_ in *implementation*,
> > just differing in how they are used?
> That was certainly true at one time. But I think the Bert Canopy went
> through a Dean-driven reform since then. Or perhaps this was planned but
> never happened. Dean?
> >3. Are the nodes (histons) in an HTree and the nodes (dsploafs)
> > in an OTree the same object, just seen from a different
> > perspective? To say it a different way, are there an equal
> > number of histons and dsploafs in an Ent, permanently paired
> > from their moment of creation? One of the documents refers
> > to red/blue butterfly shapes, leading me to believe Ent
> > nodes are composite objects, each with a histon and dsploaf
> > _interface_.
> I don't remember the terminology any more, so I'll answer in more basic
> terms. Let's call each southward pointing OTree node an ONode, and each
> northward pointing HTree node an HNode. The inter-penetration of HTrees and
> OTrees can be seen in terms of units consisting of a single H-subtree and a
> perpendicular single O-subtree attached to each other at their roots. As I
> recall, it was such a unit that was called a histon. A histon wasn't a kind
> of object, but rather a particular kind of clump of objects.
> >4. Technically speaking, canopies are not considered, by the
> > documents I've read, to be a part of the Ent, but rather a
> > data structure _over_ it. I'd like to get my terminology
> > right, so is this correct?
> We were probably ambiguous about this, but I'd say it was indeed part of the
> Ent. Perhaps we should speak separately about the Ent's internal volume vs
> the Ent's canopies, but the Ent consists of both together. This also fits
> the metaphor better -- forests have canopies.
> >5. Do the H and O trees interpenetrate at _all_ levels or only
> > at the leave/root levels? From my many readings, Mark
> > Miller's tutorial implied they only connect at the leave
> > and root levels but the red/blue butterfly concept would
> > contradict this. I suspect they connect at all levels.
> All levels. I'm surprised my tutorial implied otherwise.
> >6. Mark Miller's tutorial makes a brief mention of expanding
> > loafs, with regard to the real and sequence coordinate
> > spaces, but never goes any deeper. Aren't expanding
> > loafs really the 'hang POOM enfilades off the bottom'
> > concept from Green?
> I don't remember the 'hang POOM enfilades off the bottom' concept from
> Green, so I can't say. I believe the notion is that you only need to divide
> up the south leaves as driven by sharing differences.
> >7. At one point in a transcript it is stated that text
> > documents can have gaps or voids in the coordinate space.
> > The person who asks is told that such an ability is crucial
> > to Gold, but nothing further is said. Why is it crucial?
> I don't know why I said it was crucial, but it is a necessary consequence of
> Gold's view that all enfilades are a parameterization of generic enfilade
> code with a coordinate space.
> >8. With all the unique/cute names in Xanadu, what is the name
> > of the AVL nodes within a canopy?
> Independent of whether these are actually AVL nodes, I don't remember. Anyone?
> >9. Considering mutability and read-only storage, are histons,
> > canopies and dsploafs *immutable* or not? I don't see
> > how the splay tree of histons can be immutable, nor the
> > nodes that make up a canopy. Canopies seem to be mutable
> > since they get *marked* and *unmarked* over time.
> Internally, as a data structure, it's all mutable. At the Edition/Works
> level of external semantics, Editions are approximately immutable.
> >10. With regard to multithreading/locking, doesn't the
> > marking/unmarking of canopies, mean that there can only
> > be one entity in the Ent at a time? Doesn't this place
> > a severe bottleneck on the performance? (I need to learn
> > more re dagwood, endorsements/permissions).
> The backend runs as a singly threaded event loop. Anything else would lead
> to multi-threaded madness. For later thoughts on this issue, see
> http://www.erights.org/elib/concurrency/event-loop.html .
> >11. In Mark Miller's transcript he says that the canopies
> > get updated "just in time" but then he is interrupted
> > and never finishes the thought. When are they updated?
> I'm surprised I said this, and it doesn't correspond to my memory of the
> canopies. I don't remember anything lazy going on there.
> >12. The bert canopy is only used when going northward in
> > the H-Tree; does this mean the recorder canopy is *only*
> > used when going southward in the O-Tree?
> The bert canopy is only *read* when going north in the HTree. It is
> written southward when moving permissions and endorsements around.
> If I recall, the recorder canopy is indeed only read going south in the
> OTree, when moving permissions and endorsements around. It is written
> northward when placing recorders.
> >And two unrelated questions:
> >1. Should I be posting these questions on the Udanax mailing
> > list (i.e. are all of you subscribed?) or would you prefer
> > private correspondence for spamming/privacy reasons?
> > I'm not always sure whom to email and whom to leave out
> > of the private stuff, so I'd prefer the mailing list
> > _if_ you are on it.
> As far as I'm concerned, all of this is public. I feel confident the rest
> of us feel likewise. We have all suffered too severely from our past
> secrecy. I'm not sure what I subscribe to anymore. How about sending it
> out to Udanax and cc'ing the rest of us?
> Feel free to start by reposting your questions and my answers.
> >2. Are any of you aware of a promising microtransaction,
> > e-currency system? The billing system in Xanadu, your
> > work on E and agorics seem to need that, but none of
> > the alternatives I've researched are satisfying. E-gold
> > seems the most solid, but has a problem (IMHO) with
> > getting funds into/out of the system at a reasonable
> > transaction fee (i.e. right now they charge 6-12%).
> > It also is totally centralized, with issues there.
> Despite the problems, e-gold is the best I'm aware of. See also the Hansa
> Dollar and GoldMoney. As for centralization, no one knows how to build a
> truly decentralized issuer. It's the holy grail of money protocols, but it
> may be impossible.
> The best I know to do is to divide the center into multiple organizations
> along separation-of-duty lines, such that the risk from any one going bad is
> bounded. E-gold has done a tremendous job of that.