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Jonathan Robie wrote:
>
> What's the silver bullet? What's going to drive people away from the
> HTML and XML systems that are good enough for 90% of what people need?
> What is it going to drive them to?
Universal State Transfer? :-) Only they ain't no
transclu-whatsit in this, and they ain't gonna be:
Context Transfer Protocol (Uniform Context Transfer Protocol?)
The context transfer protocol (CTP) is an end-to-end data
transport protocol that supports manipulable distributed
hypermedia and data processing on the basis of the concept of
universal state transfer. It employs a set of abstract terms
that designate the elements of a uniform structure for
representing and transferring state, called the uniform context
framework (UCF).
In place of documents and files, CTP implements contexts,
manipulable collections of resource elements which are referred
to according to the UCF abstractions. All of the elements of a
context are assigned key values which function as links to the
servers at which the elements originate. Because all elements
are links, multiple contexts may freely reuse the same elements.
The elements of the UCF reflect a universal information
architecture which supports all the fundamental operations one
needs for managing information, including modeling, updating and
maintenance, manipulation, querying, categorizing, distribution
and dependency tracking. In this way, CTP implements the notion
of an atomic application. Fundamental information processing
functions for any application can be implemented simply by
declaring a CTP context, or by declaring multiple contexts to be
combined in a complex application. Any CTP front end interface
that surfaces the full complement of CTP functionality can be
used to browse and work with any information for any other
application served by a CTP server.
CTP is designed for scalability, providing a simple uniform
interface through the use of a small set of verbs (GET, PUT,
REMOVE and HOST) and the finite set of generic elements which
make up the UCF. CTP servers attain the status of universal
application servers in the sense that all fundamental
information management functions are provided by means of this
interface and the rest of the functions and architecture
incorporated within the protocol.
The information architecture underlying CTP affords a maximum
degree of flexibility in data processing. Entity relationships
for all applications are stored in a flat fact table form,
allowing information to be accessed and worked with rapidly,
flexibly and with implicit interoperability among all
applications. In addition, by using the UCF abstractions as
generic primitives, CTP makes possible a highly granular
procedural approach to data processing that is unimpeded by the
intricacies of entity-relationship models or the strictures of
table- or record-level distribution and/or replication.
Higher-level techniques for managing complexity, such as
set-oriented and object- oriented data processing and
programming, may be implemented on top of the CTP layer.
Instead of working with information through the representation
of diverse entities in separate physical tables, the CTP
physical data model is a generalized and denormalized structure
that directly represents relations as such. Relations
implemented under CTP are called contexts. CTP uses the
following generic abstractions to represent the elements of any
context:
Space
Location
Standpoint
Use Type
Use
Link Type
Link
Use Attribute
Link Attribute
Use Attribute Value
Link Attribute Value
Use Category
Link Category
Use Category Value
Link Category Value
These elements make up the uniform context framework (UCF), a
standard structure for representing and transferring state. CTP
assigns unique key values to each element, made up of a URL
(designating the location of a CTP server), a forward slash, and
a key value unique to that server. For example:
ctphome.org/18273645.
A general context in CTP is comprised of a use type related to a
link type. A particular context instance is designated by a
particular use of the use type, which can have any number of
links, particular instances of the link type, related to it.
This combination of use types, link types, uses, and links
describes a traditional one-to-many relationship, wherein the
various uses of a use type serve as “records” of the parent
entity type (on the “one” side), and the multiple links of a
link type serve as “records” of the child entity type (on the
“many” side).
In CTP, state is an aspect of contexts representing their
generality, and is designated in terms of the concepts of space,
location, and standpoint. Declaring a state for a CTP context
means that the context serves as a convention among all clients
and servers that participate in that state. Space represents the
notion of an abstract realm within which numerous CTP servers
participate and interoperate as they support shared contexts.
Location represents an individual CTP server. Standpoint is an
abstraction used to represent states of narrow scope hosted at
particular locations, for the purpose of independent or
provisional development work.
Generality of a state is designated by either providing key
values for space, location and/or standpoint, or leaving their
key values empty. A state representing generality across an
entire space is represented by providing a unique key value for
the space, while leaving the location and standpoint keys empty.
A state for representing universal conventions would be
designated by leaving all three key values empty. However, since
this designates no authoritative server for the state, contexts
defined within such a state cannot be managed by CTP, and would
require ratification as standards by external standards bodies,
followed by general adoption in code and practice. With CTP,
this process of fostering general adoption by means of standards
bodies becomes significantly less necessary. Instead of
presupposing that state and physical data models are so
arbitrarily complex and diverse as to necessitate such a process
in order to assure interoperability, CTP provides for universal
interoperability at the data transport level.
Traditional entity-relationship modeling entails record- and
table- level replication in distributed environments because it
binds sets of attributes to individual physical tables
representing discrete entities. Under CTP, distribution of
attributes and their values is not accomplished in the same
manner. CTP uses the UCF to distribute metadata describing the
relational organization of information across servers, while it
leaves particular attribute values at particular locations,
where CTP servers act as their authoritative hosts. User agents
and interoperating CTP servers may maintain the currency of
their local caches of attribute values according to any
algorithm appropriate to their own purposes.
Instead of binding sets of attributes to particular tables
representing particular entities, CTP uses the abstractions that
make up the UCF to describe scopes of relevance for link and use
attributes. Attributes can be declared to be relevant for all
links of a particular link type, or for all links used by a
particular use type, or for all instances of a particular use or
link regardless of general context (use type and/or link type),
or for any other of the finite number of scopes that can be
described by the possible permutations of the UCF elements. CTP
servers provide and maintain appropriate attributes and values
for various contexts according to these scopes of relevance.
CTP contexts do not presuppose or require locking mechanisms,
since whenever user agents request an occasion to modify a
context, CTP servers notify them whether the context has been
modified in whole or in part since the time of the user agent's
local copy. CTP servers may implement shared contexts as freely
interruptible or as "reservable" according to diverse governing
principles. Separate protocols may implement locking or other
"reservation" schemes on top of the CTP layer, for contexts for
which that is desired.
Message structure
- requests, responses, occasions, events
State distribution system
- metadata, attributes, values, hosts
Data structure
- denormalized
Errors / Responses
Appendix A: CTP and RDF
The correlates for RDF's subjects, predicates, and objects under
CTP are uses, link types, and links.
CTP/Use - [RdfSubject]
CTP/Link Type - [RdfPredicate]
CTP/Link - [RdfObject]
CTP moves beyond RDF's knowledge-modeling assertions by
splitting subjects into use types and uses, and then using the
combination of use types with link types to define atomic
applications, contexts which automatically provide all
fundamental information functions needed to manage information
for any application. Because CTP is designed in this manner, it
is perfectly suited for RDF applications. It simply goes beyond
the knowledge-modeling purposes of RDF and the semantic web, to
providing universal fundamental functions and implicit
interoperability among all applications.
Appendix B: CTP and REST
Roy Fielding has articulated a comprehensive set of engineering
principles which constitute an architectural style called
"representational state transfer" (REST) intended to govern
optimal Web architecture and Web application design. By
describing how CTP's implementation of universal state transfer
compares with the architectural principles of REST, we can
address its design implications in an orderly and reasonably
complete manner. The chief differences stem from the fact that
past architectural principles have presupposed the arbitrary
complexity of state and data models, and therefore have taken
certain design decisions geared toward managing complexity,
which are unnecessary within CTP.
--
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New Yorkers for Fair Use
http://www.nyfairuse.org
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