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Independent Submission M. Basaglia
Request for Comments: 9402
Category: Informational J. Bernards
ISSN: 2070-1721
J. Maas
1 April 2023
Concat Notation
Abstract
This document defines the Concat notation: a text-based language used
to describe pictures and videos whose subject includes cats,
containers, and their interactions.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This is a contribution to the RFC Series, independently of any other
RFC stream. The RFC Editor has chosen to publish this document at
its discretion and makes no statement about its value for
implementation or deployment. Documents approved for publication by
the RFC Editor are not candidates for any level of Internet Standard;
see Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9402.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document.
Table of Contents
1. Introduction
1.1. Conventions Used in This Document
2. Definition
2.1. Terminology
2.2. Grammar
3. Elements
3.1. Subjects
3.1.1. Cats
3.1.2. Partial Cats
3.1.3. Other Animals
3.1.4. Balls of Yarn
3.2. Containers
3.3. Positioning
3.3.1. Horizontal Position
3.3.2. Vertical Position
3.3.3. Multiple Repeated Objects
3.4. Changes over Time
3.4.1. Disambiguation
4. Internationalization Considerations
5. Security Considerations
6. IANA Considerations
7. Normative References
Appendix A. Examples
Authors' Addresses
1. Introduction
Cat pictures and videos are often shared across the Internet. Many
of these files display feline subjects interacting with boxes and
other containers.
Since there is currently no compact notation for describing such
media, this document details a standard notation to describe the
position and interaction of cats, containers, and related subjects
pictured in these images.
The notation language described in this document is text-based and
limits itself to the US-ASCII character encoding [RFC0020], allowing
the transfer of cat-related materials in environments with restricted
capabilities.
1.1. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Definition
2.1. Terminology
This document uses specific terms to refer to items being depicted by
the notation described herein.
To avoid ambiguity, such terms are defined as follows:
Subject: The term "subject" is used in this document to refer to the
object that is the focus in the media to be annotated. This
usually is an animate object, specifically a cat. An annotation
can have multiple subjects interacting in various ways.
Cat: A cat is a special kind of subject of feline origin. This
document will assume a house cat is present in the source media;
however, other felines are also acceptable.
Container: The term "container" is used to refer to inanimate
objects inside of which one or more subjects can be located. Most
commonly, this will be a cardboard box; however, a variety of
containers can be used.
2.2. Grammar
The grammar is defined using the ABNF notation [RFC5234].
SEQUENCE = POSITION / POSITION "=>" SEQUENCE
POSITION = ADJACENT
ADJACENT = OVER / ADJACENT "+" OVER
OVER = MULTIPLE / MULTIPLE "/" POSITION
MULTIPLE = CONCAT / NUMBER [ "*" ] MULTIPLE / NUMBER "/" MULTIPLE
CONCAT = SUBJECT [ NUMBER ] / [ PARTIAL ] CONTAINER [ PARTIAL ]
CONTAINER = "[" OPT-POS "]" / "(" OPT-POS ")"
CONTAINER =/ "{" OPT-POS "}" / "<" OPT-POS ">"
OPT-POS = [ POSITION ]
SUBJECT = CAT / 1*ALPHA / "@"
CAT = "cat" / PARTIAL
PARTIAL = "c" / "a" / "t" / "ca" / "at"
ALPHA = %x41-5A / %x61-7A
NUMBER = 1*DIGIT
DIGIT = "0" / "1" / "2" / "3" / "4"
DIGIT =/ "5" / "6" / "7" / "8" / "9"
3. Elements
3.1. Subjects
3.1.1. Cats
The standard notation for a cat is the word cat.
3.1.2. Partial Cats
When referencing cats partly inside a container, the annotation MUST
contain the full cat mark adequately split inside and outside the
container.
If a cat is only partly visible in the frame of the picture or video,
the annotation MAY only reference the visible portion of the cat.
The partial cat notations are as follows:
c: marks the head of the cat.
a: marks the body of the cat.
t: marks the tail of the cat.
ca: marks the head and body of the cat.
at: marks the body and tail of the cat.
The annotation for a partial cat SHOULD use the terms mentioned above
that best describe the portion of the cat that is being referenced.
3.1.3. Other Animals
Other animals or animate objects SHOULD be represented with a
suitable word describing the species of such animal. The cat-
specific words described in this document MUST NOT be used for non-
feline subjects.
3.1.4. Balls of Yarn
Balls of yarn SHOULD be represented with @.
3.2. Containers
When a cat or other subject is inside a container, the container
notation MUST be used. Such notation is denoted by its subject being
between brackets. The type of bracket depends on the shape of the
container as follows:
* Square brackets represent boxes or other containers with a
rectangular opening.
* Parentheses represent containers with a round opening or shape.
* Curly braces SHALL be used to represent soft containers without a
fixed shape.
Additionally, angle brackets MAY be used to group subjects outside a
container. Such annotations MUST NOT contain partial cats.
3.3. Positioning
The Concat notation only gives information about the general layout
of subjects and containers, but it does make a distinction between
horizontal and vertical positions.
The order of positional operands SHOULD follow the order in which
they appear from left to right in the source media.
3.3.1. Horizontal Position
The + operator is used to represent subjects or containers next to
each other.
3.3.2. Vertical Position
When a subject is above or on top of another, the operator / MUST be
used.
3.3.3. Multiple Repeated Objects
When multiple objects or configurations are repeated, the shorthand
notation MAY be used.
Horizontal positioning is denoted by a number followed by an optional
* and the annotation to be repeated.
Similarly, for vertical positioning, repeated objects are denoted by
a number followed by / and the annotation to be repeated.
When using such a shorthand, the number of repetitions MUST be a
positive integer.
3.4. Changes over Time
In the case of videos or other animations, a proper Concat notation
SHOULD make use of the state change operator (=>) to mark significant
changes in the cat position and major interactions.
3.4.1. Disambiguation
Subject tokens MAY be followed by an integer identifier to
distinguish specific cats, balls of yarn, or other subjects. An
annotation containing such numeric disambiguations MUST contain such
disambiguations for all cats and balls of yarn.
Since a specific subject can only appear once in a static image,
disambiguation identifiers SHOULD be used only on annotations showing
state changes.
4. Internationalization Considerations
The word cat is in English and is provided to allow transfer of
Concat notations using only the US-ASCII character encoding
[RFC0020].
Users of other languages MAY extend the alphabet and use their
localized words for cat and other animals.
Non-standard words for cats SHOULD NOT be used unless all parties
involved in the production and consumption of the Concat notation
have agreed upon a character encoding and a language prior to the
transmission of the annotation.
5. Security Considerations
A cat might find themselves in a container smaller than the perceived
volume of the cat. While this might seem to be a dangerous
situation, it's actually a natural occurrence when the cat is in its
liquid form.
Cats might chew on the cardboard of the box containing them. To
mitigate this attack, we recommend having multiple boxes to put the
cats into.
6. IANA Considerations
This document has no IANA actions.
7. Normative References
[RFC0020] Cerf, V., "ASCII format for network interchange", STD 80,
RFC 20, DOI 10.17487/RFC0020, October 1969,
<https://www.rfc-editor.org/info/rfc20>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
Appendix A. Examples
This appendix provides some examples of the Concat notation.
[cat]
Figure 1: A Cat in a Box
[cat] + cat
Figure 2: A Cat in a Box Next to a Cat Not in a Box
cat / [cat]
Figure 3: A Cat over a Box Containing Another Cat
[c]at
Figure 4: A Cat with Its Head inside a Box
3 * cat
Figure 5: 3 Cats Side by Side
3 / cat
Figure 6: 3 Cats on Top of Each Other
cat + cat / [cat]
Figure 7: A Cat Standing Next to a Box That Has a Cat on Top and
inside of It
<cat + cat> / [cat]
Figure 8: Two Cats Standing on a Box with Another Cat inside of It
cat1 + [cat2] => cat2 + [cat1]
Figure 9: A Cat inside a Box and a Cat outside Swap Places
Authors' Addresses
Mattia Basaglia
Email: glax@dragon.best
URI: https://dragon.best/
Joep Bernards
Email: joep@duali.xyz
Joost Maas
Email: J.f.w.maas@tue.nl