Glossary of Common Xanadu Terms

CoordSpaceTheory?

http://www.sunless-sea.net/wiki/Definitions/CoordSpaceTheory

KTree?

Derived from an article in Dr. Dobbs. More info coming soon...

bert

Similar to a file handle, it is named after the great mathematician Bertrand Russell, who spent his life trying to introduce consistency into mathematics. A bertD of a particular editionD of a workD is obtained, in either a read or write mode before operating upon a document, and released thereafter.

"Berts are the soul of a document and represent the discrete, persisting identity behind the changing representations of that identity. As changes are made, a document visits different states (represented by new Stamps), and whenever a particular state is blessed with a BertD? hopped from a predecessor StampD? we refer to the result as a new "editionD" of the original document.

When a document is replicated a new BertD? is created representing a new and separate identity; we refer to this as a "variation" on the original document, anticipating a distinct intent by providing a distinct identity and state/edition history capability (note that the term "variation" is somewhat presumptuous, but not overly so since it fits our reasonable expectation of actual changes representing a new intent). "

References:

• Version Aversion

blast

Equivalent to an exception, as in raising of an exception in C++ or Python. Where the exception is caught, as in a exception or catch statement in the language, is called a blastshield or just shield in Udanax-gold.

A blast can be triggered deliberately by a bomb.

bomb

A bomb triggers a blast. It appears to be referring to code that raises exceptions deliberately. "Planting a bomb" is the act of putting in exception raising code. --JohnDougan

canopy

a set of disjoint trees that forms a layer over the core of the Ent. There are two canopies in the Ent; the Bert canopy, which tracks changes in the content along the space dimension, and the Recorder canopy, which tracks changes along the time dimension (i.e. the historical trace).

club

a roster of users in the Udanax-gold access control system. There are three clubs: readers, writers and owners.

crum

A piece of a Loaf? Yes. A combination of disp, wid and either a pointer to a lower-level loaf, or bottom-level leaf contents. See EnfiladeTheory? and loaf.

Named after bread crumbs, the Crum River which runs through or near Swarthmore College, and, "Code, Recursive and Universal, for Meanders." Meanders being, essentially, spans of text within editions. Someone anonymous in Mark Miller's Ent class says it also means "chickens running under mud."

dead pan

docuverse

the complete set of all documents in the entire Xanalogical storage system.

edition

a particular frozen representation of a document or work. Udanax-gold sought to avoid the use of the confusing version or revision terms.

endorsement

enfilade

a type of B-tree structure fundamental to Udanax-green. It appears in Udanax-gold as well, but in a less important role. (But see Ent.)

See EnfiladeTheory?.

For POOM enfiladeD, see Permutation Of Order Matrix.

ent

The basic data structure of Udanax Gold., It can be thought of as a mutated enfilade, and as a data structure the views of which are virtual enfilades.

To understand ents, you should understand enfilades first, so see EnfiladeTheory?.

The new thing the ent does is that you can access it from the bottom or the top to get inverse mappings. (Only now that the two are symmetrical, they're renamed North and South.) That means that nodes can have multiple connections in both North and South directions. Look at EntTheory after reading EnfiladeTheory?.

The ent was originally conceived by Eric Drexler (as was at least one Udanax Green enfilade). I don't know whether he invented the Canopy. The ent is named after the "the walking trees with great memory in J.R.R. Tolkien's Lord of the Rings", according to Ted Nelson.

: --SteveWitham

flock

Copied from a forum message

Objects migrate to and from the disk in groupings called "flocks". The flock is the minimum granularity at which objects are purged from core and restored from disk. A flock consists of exactly one shepherd and an arbitrary number of sheep (as long as the entire flock is guaranteed of fitting in a single snarf? Is this true? Michael? Dean? How can we be confident this condition is satisfied?). A "sheep" (what is the singular?) is simply a "COPY(X):" object which needn't be at all cognizant of the disk. The single shepherd in a flock is "representative" of the flock as a whole--the only inter-flock pointers are to shepherds.

This means that the only on-disk pointers to a sheep must be from objects within the same flock as this sheep. If a sheep is an EQObject? there is no problem, because a hash table that points to it must be within the same flock. Given that hash-indexed structures rehash when being read back in off disk, the flock will always be using valid hashes during its stay in core.

--JohnDougan

fm

FM stands for "Frontend Magic".

It appears to be a front-end codebase(?) for developers and was written in Smalltalk/X++. --JohnDougan

formic

some type of preprocessor tool used to convert SmallTalk? source into the Udanax style of C++, called XPP. XPP provided garbage collection and persistence mechanisms to the C++ language.

innerloaf

Each inner loaf just holds a distinction region. The left child is all the data inside the distinction, the right child is all the data outside the distinction

ktree

An enfiladeD-like data structure described in an article in Dr. Dobbs. See KTrees?.

More info coming soon...

http://www.xanadu.com.au/mail/udanax/msg00056.html(approve sites)

loaf

What other people would call a node in a tree. A block of data that Contains Crums, the basic little data blobs in enfilades. See EnfiladeTheory?.

montage

an example front-end for Udanax-gold, written in Scheme, a flavor of Lisp.

moose

Taken from a message by Eric Hill on December 31/1988

Before I proceed further, I should mention that because of an earlier observation by Robin Hansen, a new element has been added into the computational lexicon: "moose." A moose is an inadequately addressed design issue that is potentially very large and very nasty. It could be thought of as a metabug, as it is a problem that exists before code is even written, and could therefore produce bugs (or spoilage) if unresolved. The origin of this term comes from a design meeting where Robin accepted the task of logging issues that had been swept under the rug. At one point he made a comment to the effect that, "it looks like you've swept a whole moose under there." In the Xanadu design effort, this term has proved invaluable--the language, however, may never be the same. --JohnDougan

necromancer

Person that it can raise from the dead, or at least manipulate the dead... --JohnDougan

newmath

New Math

nguyentest

this is for nguyentest

orgl

derived from ORGanizing? eLement, it refers to a particular arrangement of bytes, usually text.

In udanax-green, an ORGLD is a 2-dimensional enfilade representing a permutation matrix, or POOM.

In udanax-gold, ORGLs? are the same as OTrees?, also called an Edition of a Work or document. In udanax-gold, they may have the following states:

• complete or full -- has all the data that it will ever contain.
• partial -- has some areas in its coordinate space that are not associated with data yet, but may be in the future.
• ready -- contains some data (associated with positions). This can either be a partial orgl with some data in it or a complete orgl. I'm not sure what this should mean for a complete but empty orgl.
• unready -- partial but with no data in it.

patriarch

the ranking shepherdD...

Does the Patriarch manage the Shepherds?

recorder

a component of Udanax-gold that resides in one of the two canopies of the Ent, and reports on changes within the Ent. It is somewhat equivalent to a trigger in an SQL database system.

sensor

an obsolete term, renamed to recorder because audibly 'sensor' sounds like censor. It is a component of Udanax-gold that resides in one of the two canopies of the Ent, and reports on changes within the Ent. It is somewhat equivalent to a trigger in an SQL database system.

sheep

A sheep appears to be a component of the Xanadu gold persistence mechanism. It is the on-disk representaton of a single object. A sheep is contained in a flock, which has a shepherd. --JohnDougan

Copied from a forum message

A "sheep" (what is the singular?) is simply a "COPY(X):" object which needn't be at all cognizant of the disk.

shepherd

some element of the Udanax-gold persistence mechanism responsible for activating and deactivating objects re permanent storage.

The single shepherd in a flock of sheep is a "representative" of the flock as a whole -- the only inter-flock pointers are to shepherds. --JohnDougan

shield

an exception-catcher, as in the exception: or catch statement of Python or C++. A shield catches and recovers from a blast (exception) in a lower portion of the Xanadu source code.

snarf

From a forum message by Eric Hill on Dec 31, 1988.

Snarfs are units of data exchange that grew out of typical disk data transfer rates compared to typical seek times. A snarf has a size that is optimized for the transfer to seek ratio of the mass storage device used-- roughly a track. By reading a track-sized chunk of data structure into main memory, one is likely to get a large amount that will be needed immediately, with virtual no additional cost for bringing in the unneeded parts. --JohnDougan

stamp

tapestry

Tapestry is a user interface for Xanadu Gold.

TapestryD? was designed to optimize the presentation of evolving collections of documents. It was designed to be a smooth scrollling system without the chunkiness present in systems like HyperCard??. --JohnDougan

References:

• Tapestries of Hyperdocuments by Marc Steigler

tumbler

An early type of coordinate space, used primarily in Udanax-green. It appears in Udanax-gold as well, as part of the taxonomy of possible coordinate spaces.

A tumbler is like the number assigned in the dewey decimal system or in SCCS style revision numbers. An example tumbler would be: 1.1.4.5.6.0.3.4.67.0.888.33.22.1.0.2234

A tumbler is an example of a transfinite number. The advantages of this as a numbering system for Xanadu addressing are:

1. There is always a tumbler between two different tumblers, so insertions never require renumbering.

2. A set of tumblers can be ordered.

3. The tumblers can be arranged to form a hierarchy, making it easy to specify all tumblers that start with a shorter tumbler. This is used in the Xanadu green system for queries like "all documents of this user". This is also useful for delegating assignment authority, like in the DNS.

4. Arithmetic can be done with tumblers. Specifically addition and subtraction, making it possible to specify ranges of tumblers.

In Xanadu green, the tumblers are in the form (with all components specified): 1.<node>.0.<user>.0.<document>.0.<content> where each <piece> is a tumbler fragment.

So the tumbler specifing the 3rd text byte of the document 10.3.5.6 for user 77.2334556.78.2 on the node 99.432 would look like 1.99.432.0.77.2334556.78.2.0.10.3.4.6.0.1.3 . Shorter forms are allowed as are tumbler differences, so asking for all data starting from 1. with an extent of 1 will give you everything in the system. Asking for all data starting from 1.99.432.0.77.2334556.78.2 with an extent of 0.0.0.0.0.0.0.1 will give you all of the documents belonging to user 1.99.432.0.77.2334556.78.2.

    --JohnDougan

urdi

Taken from a forum message by Eric Hill on Dec 31, 1988.

The Unusually Reliable Disk Interface developed by Michael Mc Clary gives us a degree of incremental recovery from system failures that we have long been wanting. As with any heavily cached system, Xanadu runs the risk of having an inconsistent data structure on the disk after crashes and power failures. Buffering in most operating systems and high-end disk drives only aggravate this problem. The URDI allows a consistent, although not necessarily current disk data structure to be achievable after when restarting the system after some, but not all failure modes. Some the modes that we are not protected against are spiral writes and head crashes. The metaphorical model that Michael has used is Fibber Mc Gee's closet. The closet represents the main storage area on the disk where most reads take place, and a consistent data structure is more or less guaranteed during execution of user requests. Writes, however, go through a staging area on their way to the closet, where groups of snarfs are placed in temporal order. At the end of each group is a marker indicating that if all of the staging area up to that point has been put in the closet, the disk will be consistent. After a failure, this area will be processed before acknowledging any requests. While this will result in some delay at system restart, it is immensely faster than reevaluating the entire transaction log. --JohnDougan

waldo

a remote-procedure-call stub; the part of the frontend/backend protocol that resides on the client and provides the remote API to Xanadu.

A waldo is also the name for remote manipulation equipment of the type that copies the hand/arm motions of the user.

work

another name for document, representing a continuum of frozen editions. In Udanax-green they were called documents and versions, but were renamed to works and editions in Udanax-gold for clarity of meaning.