FeBe Protocol


Metasyntax

To be able to discuss the syntax and semantics of the FeBe Protocol, we need a metasyntax.

Terminal symbols are printed using a fixed typeface. Non-terminal symbols are written in cursive style. Subscripted labels are only for documentation. Descriptions of commands refer to arguments using these labels.

The brackets `[' and `]' are meta-syntactic symbols. They designate optional and/or repeating sequences.

[ symbol ]? zero or one occurrence of symbol

[ symbol ]* zero or more occurrences of symbol

[ symbol ]+ one or more occurrences of symbol number * [ symbol ] number followed by number occurrences of symbol The arrow `' specifies a call and return sequence in the protocol: call result | error For a more detailed discussion, please refer to the introduction of "Appendix A - FeBe Protocol Syntax".

Lexical Components

Special Characters newline ::= This is the character 128 or A16, often represented as '\n' in C.

delim ::= `
~' | newline

digit
::= `0' | `1' | `2' | `3' | `4' | `5' | `6' | `7' | `8' | `9'

byte ::= Any 8 bit value
The FeBe Protocol uses 8 bit ASCII characters without parity. Commands that transfer data-bytes transfer count delimited sequences of bytes. The protocol does not reserve any escape codes within data transmissions.

Errors error ::= `?' Calls to the backend that succeed return their command number followed by any return values. Calls that fail for any reason return only the single character `?'.

Tumblers number ::= [ digit ]+ delim

exponent
::= [ digit ]+

tumbler ::= exponent [ `
.' [ digit ]+ ]* delim
A tumbler is an ordered sequence of numbers; for example, "123.45.0.89.1" or "32.17".

Each number within a tumbler is called a "tumbler digit".

In the tumbler "123.45.0.89.1" the underlined parts of the tumbler are "tumbler digits". The zero (`.0.') tumbler digit (when not in the exponent position) is only used as a separator in address tumblers. + In the 88.1x implementation of the FeBe protocol each tumbler digit has to be in the range of 0 to 4,294,967,295 (232-1). Comparison and arithmetic operations on tumblers align tumbler-digits from the left. Since tumblers used as widths for spans often start with many zeroes, FeBe uses a compact representation for tumblers. The first tumbler digit in the representation is the number of zero tumbler digits at the beginning of the tumbler. Thus, the tumblers "32.2" and "0.0.0.14.5" are represented by "0.32.2" and "3.14.5." This leading tumbler digit is referred to as the exponent of the tumbler. + In the 88.1x implementation of the FeBe protocol there may be a maximum of 11 non-zero tumbler digits plus exponent in any one tumbler. This restriction will be eliminated in a later release.

  id ::= tumbler
These tumblers are global identifiers. IDs can refer to any Udanax Green objects. (See the chapter "Addressing" for more details.) vaddr ::= exponent `.' [ digit ]+ [ `.' [ digit ]+ ]? delim These tumblers are relative to a given document, so they only have one or two digits. The first digit determines the space (1=text, 2=link). The second digit determines the location within that space.

Groups span ::= tumblerstart tumblerwidth A span specifies a range of Udanax Green objects in the global address space. Spans include all objects between tumblerstart inclusive and tumblerstart plus tumblerwidth exclusive. (See the chapters "Tumbler Arithmetic" and "Addressing".) vspan ::= vaddrstart vaddrwidth A vspan specifies a range of data-bytes and/or links within a given document. spec ::= `s' delim span

| `v' delim doc-id number * [ vspan ]

spec-set ::= number * [ spec ]
A spec-set specifies a possibly discontinuous set of Udanax Green objects. shared-span ::= tumblerstart-1 tumblerstart -2 tumblerwidth A shared-span indicates that the span specified by tumblerstart-1 and tumblerwidth represents the same Udanax Green objects as the span specified by tumblerstart -2 and tumblerwidth. Only the version comparison operation returns shared-spans.

Document Contents string ::= `t' number * [ byte ] Strings wrap data-bytes for transmission between the frontend and the backend. + In the current implementation (88.1x) there is a maximum of 950 data-bytes in a single string. This limitation will be removed in future releases. It is not recommended to even try to write longer strings to the backend.

  contents ::= string | idlink
Documents contain data-bytes and links. A frontend can retrieve a span that contains both.

Command Codes create-new-document ::= `11' delim

create-new-version
::= `13' delim

open
::= `35' delim

close
::= `36' delim

create-link
::= `27' delim

retrieve-doc-vspan
::= `14' delim

retrieve-doc-vspanset
::= `1' delim

retrieve-v
::= `5' delim

follow-link
::= `18' delim

retrieve-endsets
::= `28' delim

find-links-from-to-three
::= `30' delim

show-relations-of-2-versions
::= `10' delim

find-docs-containing
::= `22' delim

insert
::= `0' delim

copy
::= `2' delim

rearrange
::= `3' delim

delete-vspan
::= `12' delim

quit
::= `16' delim

x-account
::= `34' delim

create-node-or-account
::= `38' delim
Creation and Access

create-new-document 11 create-new-document create-new-document iddoc| error Create a new document under the account and node of the user who issued the request. Return the global identifier for the document.

This request creates the document but does not open it for access; you must issue an open request (see below) to access the data in the new document.

create-new-version 13 create-new-version idold-doc create-new-version idnew-doc| error Return the identifier of a new copy of idold-doc. idnew-doc contains the same data and links as idold-doc. Links to those contents are visible from either document.

This request creates the document but does not open it for access; you must issue an open request (see below) to access the data in the new document.

open 35 mode ::= `1'read-only delim | `2'read-write delim

copy-switch
::= `1'fail-on-conflict delim | `2'copy-on-conflict delim | `3'always-copy delim

open id
doc
mode copy-switch open idnew-doc | error
Open iddoc for access using mode. Mode can be read-only or read-write. Read-only capability for a document can be shared. Read-write capability is exclusive. Two situations cause conflict: a request for write access on an already open document, or a request for read access to a document already open read-write. When contention arises, the backend can return a copy of the document or fail. The copy-switch determines the circumstances in which the backend makes a copy. iddoc and idnew-doc differ only if open makes a copy. Command descriptions which require already open documents for their arguments will be so noted. Open for read-write satisfies the requirement "Must be open for reading".

close 36 close iddoc close | error Close iddoc. All opened documents must be closed. Multiple opens of a document must balanced by the same number of close calls. A loss of connection between the frontend and backend or a quit command is the same as closing all documents and then doing a quit.

create-link 27 create-link iddoc spec-setfrom spec-setto spec-setthree

create-link idlink | error
Create a link with the specified end-sets and return its identifier. The new link is appended to the link space of iddoc . iddoc is the home for the idlink . iddoc must already be open for writing.

Content Retrieval

retrieve-doc-vspan 14 retrieve-doc-vspan iddoc retrieve-doc-vspan vspan | error Return the vspan describing the contents of iddoc , including its links. The width of the span reflects either the number of links or the number of data-bytes if there are no links. iddoc must already be open for reading.

retrieve-doc-vspanset 1 retrieve-doc-vspanset iddoc retrieve-doc-vspanset number * [ vspan ]

| error
Return a vspan describing each space in iddoc . If either the data or link space is empty, its vspan is left out. iddoc must already be open for writing.

retrieve-v 5 retrieve-v spec-set retrieve-v number * [ contents ] | error Retrieve data and links from the backend. The spec-set can include document identifiers, text ranges, and link identifiers. The information returned follows the order of the spec-set. All the documents in spec-set must be open for reading.

follow-link 18 end-switch ::= `1'from delim | `2'to delim | `3'three delim

follow-link end-switch id
link
follow-link spec-setend | error
Return an end-set of idlink . end-switch determines the end-set returned.

retrieve-endsets 28 retrieve-endsets spec-setcontents

retrieve-endsets spec-setfrom spec-setto

spec-setthree
| error
Describes where links attach to contents. Each returned spec-set describes the union of all end-sets of the given type that attach to the supplied spec-setcontents.

Connection Retrieval

find-links-from-to-three 30 home-spec ::= number * [ iddoc]

find-links-from-to-three spec-set
from spec-setto spec-setthree home-spec

find-links-from-to-three number * [ idlink ]

| error
Return the IDs of all links whose end-sets overlap the given from, to, three, and home set restrictions. All end-sets must satisfy their respective constraints. A set containing the entire docuverse places no restriction.

show-relations-of-2-versions 10 show-relations-of-2-versions spec-set1 spec-set2

show-relations-of-2-versions number * [ shared-span ]

| error
Structurally compare the two sets of contents. Return a list describing the shared contents; i.e., contents derived from the same source through versioning or edit operations. Identical sections entered independently are not considered shared because they came from different sources. (See the chapter "Versions".) All documents mentioned in the spec-sets must be open for reading

find-docs-containing 22 find-docs-containing spec-set

find-docs-containing number * [ iddoc ]

| error
Return identifiers for all documents that include any of the contents specified by the argument. All documents with contents in spec-set must be open for reading.

Editing

Editing must be done within the backend to allow structural comparison and proper interaction of editing operations and link connections.

insert 0 insert iddoc vaddr number * [ string ] insert | error Insert text at vaddr in iddoc . iddoc must be open for writing.

copy 2 copy iddoc vaddr spec-set copy | error Virtually copy the contents specified by the spec-set to vaddr in iddoc . iddoc must be open for writing. All documents with contents in spec-set must be open for reading.

rearrange 3 cut-count ::= `2' delim | `3' delim | `4' delim

rearrange iddoc
cut-count * [ vaddr ] rearrange | error
Transpose large blocks of characters within doc. The number of vaddrs (cut-count) determines the operation. If cut-count equals 2, delete the contents from vaddr1 to vaddr2. If cut-count equals 3, swap the contents from vaddr1 to vaddr2 with the contents from vaddr2 to vaddr3. If cut-count equals 4, swap the contents from vaddr1 to vaddr2 with the contents from vaddr3 to vaddr4. The first vaddr specifying a range must be less than or equal to the second vaddr for that range. iddoc must be open for writing.

delete-vspan 12 delete-vspan iddoc vspan delete-vspan | error Remove the bytes specified by vspan from iddoc . iddoc must be open for writing.

Session Control

Frontends and backends initially negotiate about the protocol they will use. (The protocol negotiation for a session and some of the FeBe commands are demonstrated in the chapter "FeBe Example".)

quit 16 quit quit Terminate the connection between the frontend and the backend. If appropriate, the backend saves and terminates. Quit never returns an error.

x-account 34 x-account idaccount x-account | error The backend associates account with the current connection and frontend. It causes the current user to be considered the owner of account. The multi-user backend requires that this command be sent from within the standard login sequence. You can only login once per session.

Administration

create-node-or-account 38 create-node-or-account idaccount create-node-or-account idaccount

| error
Declare that account is a legal account or node. If account is an account tumbler, then the backend creates the account. If it is a node tumbler, then the backend reassigns its own address to account.

Null Command

null-command - delim A delimiter sent by the frontend when the backend expects a command is ignored by the backend.