1、Reference numberISO/IEC 8632-4:1999(E)ISO/IEC 1999INTERNATIONALSTANDARDISO/IEC8632-4Second edition1999-12-01Information technology Computergraphics Metafile for the storage andtransfer of picture descriptioninformation Part 4:Clear text encodingTechnologies de linformation Infographie Mtafichier de
2、stockageet de transfert des informations de description dimages Partie 4: Codage en clair des textesAdopted by INCITS (InterNational Committee for Information Technology Standards) as an American National Standard.Date of ANSI Approval: 10/12/00Published by American National Standards Institute,25 W
3、est 43rd Street, New York, New York 10036Copyright 2002 by Information Technology Industry Council (ITI).All rights reserved.These materials are subject to copyright claims of International Standardization Organization (ISO), InternationalElectrotechnical Commission (IEC), American National Standard
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10、 reservedISO/IEC 8632-4:1999(E) ISO/IEC 1999 All rights reserved iiiContents Page1 Scope12 Conformance.13 Normative references .24 Notational conventions 25 Entering and leaving the metafile environment.25.1 Generic clear text and instantiations25.2 Implicitly entering the metafile environment25.3 D
11、esignating and invoking the CGM coding environment from ISO 2022 .36 Metafile format.36.1 Character repertoire36.2 Separators46.2.1 Element separators.46.2.2 Parameter separators.56.2.3 Comments in the metafile 56.3 Encoding of parameter types.56.3.1 Integer-bound types56.3.2 Real-bound types66.3.3
12、String-bound types.76.3.4 Enumerated types.86.3.5 Derived types.86.3.6 Bitstream datatype96.3.7 Structured data record operands96.4 Forming names .96.4.1 Words deleted .96.4.2 Words added .106.4.3 Words used unabbreviated106.4.4 Abbreviations10ISO/IEC 8632-4:1999(E)iv ISO/IEC 1999 All rights reserve
13、d6.4.5 The derived element names.127 Encoding the CGM elements .177.1 Encoding delimiter elements.177.2 Encoding metafile descriptor elements187.3 Encoding picture descriptor elements257.4 Encoding control elements287.5 Encoding graphical primitive elements307.6 Encoding attribute elements367.7 Enco
14、ding escape elements427.8 Encoding external elements 437.9 Encoding segment control and segment attribute elements.437.10 Encoding application structure descriptor elements458 Clear text encoding defaults459 Profile encoding rules, proforma, and Model Profile 469.1 Encodings469.2 Metafile defaults46
15、9.3 Profile Proforma tables (PPF)46Annex A (normative) Clear text encoding dependent format grammar.48Annex B (informative) Clear text encoding example .49ISO/IEC 8632-4:1999(E) ISO/IEC 1999 All rights reserved vForewordISO (the International Organization for Standardization) and IEC (the Internatio
16、nal Electrotechnical Commission)form the specialized system for worldwide standardization. National bodies that are members of ISO or IECparticipate in the development of International Standards through technical committees established by therespective organization to deal with particular fields of
17、technical activity. ISO and IEC technical committeescollaborate in fields of mutual interest. Other international organizations, governmental and non-governmental, inliaison with ISO and IEC, also take part in the work.International Standards are drafted in accordance with the rules given in the ISO
18、/IEC Directives, Part 3.In the field of information technology, ISO and IEC have established a joint technical committee, ISO/IEC JTC 1.Draft International Standards adopted by the joint technical committee are circulated to national bodies for voting.Publication as an International Standard require
19、s approval by at least 75 % of the national bodies casting a vote.Attention is drawn to the possibility that some of the elements of this part of ISO/IEC 8632 may be the subject ofpatent rights. ISO and IEC shall not be held responsible for identifying any or all such patent rights.International Sta
20、ndard ISO/IEC 8632-4 was prepared by Joint Technical Committee ISO/IEC JTC 1, Informationtechnology, Subcommittee SC 24, Computer graphics and image processing.This second edition cancels and replaces the first edition (ISO/IEC 8632-4:1992), which has been technicallyrevised. Note that the previous
21、edition of ISO/IEC 8632-4, published in 1992, was a first edition but second editionwas indicated by error on its cover page and in the foreword.ISO/IEC 8632 consists of the following parts, under the general title Information technology Computer graphics Metafile for the storage and transfer of pic
22、ture description information: Part 1: Functional specification Part 3: Binary encoding Part 4: Clear text encodingAnnex A forms a normative part of this part of ISO/IEC 8632. Annex B is for information only.NOTE In previous editions of ISO/IEC 8632, Part 2 defined a Character Encoding. Part 2 was wi
23、thdrawn in 1998, due to its lackof implementation and use.ISO/IEC 8632-4:1999(E)vi ISO/IEC 1999 All rights reservedIntroduction0.1 Purpose of the clear text encodingThe Clear Text Encoding of the Computer Graphics Metafile (CGM) provides a representation of the Metafilesyntax that is easy to type, e
24、dit and read. It allows a metafile to be edited with any standard text editor, using theinternal character code of the host computer system.0.2 Primary objectivesa) Human editable: The Clear Text Encoding should be able to be hand edited or, if desired, hand constructed.b) Human friendly: The Clear
25、Text Encoding should be easy and natural for people to read and edit. Althoughwhat is easiest and most natural is a subjective judgment that varies among users, contributing factors such asease of recognition, ease of remembering, avoidance of ambiguity, and prevention of mistyping have all beencons
26、idered.c) Machine readable: The Clear Text Encoding should be able to be parsed by software.d) Suitable for use in a wide variety of editors: The Clear Text Encoding should not have any features that makeit difficult to edit in normal text editors.e) Facilitate interchange between diverse systems: T
27、he Clear Text Encoding should be encoded in such a wayas to maximize the set of systems which can utilize it. No assumptions should be made as to word size orarithmetic modes used to interpret the metafile.f) Use standardized abbreviations as much as possible: Where language encoding of other graphi
28、cs standardshave established standard abbreviations, or where common practice in the data processing and graphicsindustries has established well known abbreviations, these abbreviations are used. In accordance with theprinciple of “least astonishment”, this approach should minimize the time needed t
29、o learn to use this encoding.0.3 Secondary objectivesBecause the other CGM encoding (the CGM Binary Encoding) is targeted toward CPU efficiency and informationdensity, these objectives are considered of secondary importance for the CGM Clear Text Encoding.0.4 Relationship to other International Stan
30、dardsThe set of characters required to implement the Clear Text Encoding is a subset of those included in nationalversions of ISO/IEC 646. Any character set that can be mapped to and from that subset may be used to implementthe encoding.For certain elements, the CGM defines value ranges as being res
31、erved for registration. The values and theirmeanings will be defined using the established procedures (see ISO/IEC 8632-1, 6.12.)INTERNATIONAL STANDARD ISO/IEC 8632-4:1999(E) ISO/IEC 1999 All rights reserved 1Information technology Computer graphics Metafile for thestorage and transfer of picture de
32、scription information Part 4:Clear text encoding1 ScopeThis part of ISO/IEC 8632 specifies a clear text encoding of the Computer Graphics Metafile. For each of theelements specified in ISO/IEC 8632-1, a clear text encoding is specified. Allowed abbreviations are specified. Theoverall format of the m
33、etafile and the means by which comments may be interspersed in the metafile is specified.This encoding of the CGM allows metafiles to be created and maintained in a form which is simple to type, easy toedit and convenient to read.2 ConformanceConformance of metafiles to ISO/IEC 8632 is defined in te
34、rms of profiles. A metafile conforms to this encoding if itconforms to a profile and meets the following criteria:Gbe Each metafile element described in this part shall be encoded in the manner described in this part of thisInternational Standard and a profile.Gbe Metafile elements which are not def
35、ined in Part 1 or in this encoding are all encoded using the GENERALIZEDDRAWING PRIMITIVE or ESCAPE metafile elements as appropriate. According to the profile rules of Part 1(see clause 9, subclause 9.5.2.8), such elements shall either be profile defined or registered, in order that theprofile be va
36、lid. Inclusion of private elements is not permissible in a valid profile of ISO/IEC 8632 and thisencoding.Gbe Values of index parameters, which are used as enumeration selectors from lists of implicitly defined attributevalues, shall either be standard, registered, or profile defined. The standard a
37、nd registered values are all non-negative, and the profile-defined shall be negative. Use of private, implicitly-defined negative index valueswhich are not profile defined is not permissible in a valid profile of ISO/IEC 8632 and this encoding.Gbe Values specified as being “reserved for registered v
38、alues“ shall not be used unless their meaning has beenregistered or standardized.Gbe All characters in the metafile shall be from the enumerated character repertoire (see 6.1), except for thosewithin a parameters of type String and String Fixed, eligible parameters within specific data records, andf
39、ormat effectors as described in 6.1.Gbe Numbers shall be formatted as defined in 6.3.1 and 6.3.2.Gbe Inclusion of non-graphical data in the metafile shall be accomplished with the APPLICATION DATA element orwith the APPLICATION STRUCTURE ATTRIBUTE element.See clause 9 for additional conformance info
40、rmation about this encoding.ISO/IEC 8632-4:1999(E)2 ISO/IEC 1999 All rights reserved3 Normative referencesThe following normative documents contain provisions which, through reference in this text, constitute provisions ofthis part of ISO/IEC 8632. For dated references, subsequent amendments to, or
41、revisions of, any of thesepublications do not apply. However, parties to agreements based on this part of ISO/IEC 8632 are encouraged toinvestigate the possibility of applying the most recent editions of the normative documents indicated below. Forundated references, the latest edition of the normat
42、ive document referred to applies. Members of ISO and IECmaintain registers of currently valid International Standards.ISO/IEC 646:1991, Information technology ISO 7-bit coded character set for information interchange.ISO 2022:1986, Information processing ISO 7-bit and 8-bit coded character sets Code
43、 extension techniques.4 Notational conventionsUnbracketed strings are terminals of this grammar. They appear in valid Clear Text data streams exactly asindicated in the specifications of this part, except for allowable variations on case and null characters describedbelow.Bracketed strings are eithe
44、r non-terminals (with further productions given), character symbol names (such asCOMMA), or parameters of the CGM element in the form (see ISO/IEC 8632-1 for further explanation ofthese items).“:=“ is read as “becomes“ or “is realized as“.* = star closure (0 or more occurrences).+ = plus closure (1
45、or more occurrences).o = optional (exactly 0 or 1 occurrences).= parameter type x with meaning y= exactly one of x or y. = a comment (not part of the production)(n) = exactly n occurrences, n=0,1,2,.SPACES are used for readability in the grammar description; SPACES in the actual metafile are indicat
46、ed throughthe separator productions given below.The metasymbols used in describing the grammar do not appear in the actual metafile.5 Entering and leaving the metafile environment5.1 Generic clear text and instantiationsThe Clear Text Encoding is described in a generic fashion that permits it to be
47、used with any character set capableof representing those characters enumerated in the Character Repertoire (see part 1, 6.7.3.2). An instantiation ofthe Clear Text Encoding is specified by defining the character set and coding technique to be used (for example,standard national character sets based
48、on ISO/IEC 646, non-standard character sets such as EBCDIC, etc).It is recommended that an instantiation of the Clear Text Encoding bound to the standard national character setbased on ISO/IEC 646 be used in order to maximize portability of Clear Text metafiles between diverse systems.This also prov
49、ides an encoding which can be incorporated into an ISO 2022 text environment as a complete code,to permit intermixing of text and graphics for applications which place a high priority on human readability.5.2 Implicitly entering the metafile environmentThe Clear Text coding environment may be entered implicitly by agreement between the interchanging parties. Thisis suitable only if there is not to be any interchange with services using other coding techniques, and if it is knownby prior agreement which instantiation of the syntax
