MIMESGML Working Group D. Stinchfield INTERNET-DRAFT EBT, Inc. Expires August 22, 1996 February 22, 1996 Using SGML Open Catalogs and MIME to Exchange SGML Documents Status of this Memo This document is an Internet-Draft. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or made obsolete by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress". To learn the current status of any Internet-Draft, please check the "1id-abstracts.txt" listing contained in the Internet-Drafts Shadow Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast). Distribution of this document is unlimited. Please send comments to the HTTP working group at . Discussions of the working group are archived at ftp://ftp.naggum.no/pub/archives/sgml- internet. Abstract This proposal describes how SGML Open catalogs and MIME mechanisms are used to exchange SGML documents on the World Wide Web, or via email. Using the extension mechanism provided by Technical Resolution 9401:1995 (TR9401) [10]- TR9401 contains the technical description of SGML Open catalogs - this proposal describes new catalog keywords required for SGML document interchange. In addition, Uniform Resource Locators (URL) [8] are used to allow greater flexibility in the addressing of storage objects. This flexibility is intended to allow addressing of storage objects encapsulated in MIME messages, or addressable via the World Wide Web. A MIME body part containing an SGML Open catalog is tagged with the content type "application/sgml-open- catalog" [5]. Stinchfield [Page 1] INTERNET-DRAFT SGML Open Catalogs and MIME 2/21/96 Revision History Changed Application/Catalog to Application/SGML-Open-Catalog. Changed the syntax of Notation and added more to the description. Added ENCODING and SYSTEM keywords. Removed the keywords: CHARSET, BASESET, and CAPACITY. Will assume that the public id's used to define them in the SGML declaration will be unique within the catalog. Changed BASEURL to BASE and added to the definition so that BASE can now be either an absolute URL or an absolute filename. Also described is how multiple BASE catalog entries are used. Added a better description of how system identifiers are to be handled. TR9401:1995 is being referenced instead of TR9401:1994. User-define keywords are no longer required to begin with "X-" but it is strongly recommended. Added appendix D, public identifiers for Notations. Added an attribute to Semantics called "title". Added "Usage Guidelines" section. Removed information that is repeated from TR9401. This includes keyword descriptions and parts of the grammar. Replaced Catalogs with `SGML Open Catalogs' in the title. Require OVERRIDE and ENCODING to have at least one attribute in a catalog entry. Fix FPI for ISONUM in appendix B. Changed ISO publication numbers from "xxxx-yyyyy" to "xxxx:yyyy" format. Changed the name of the SYSTEM keyword to MAPSOI. Stinchfield [Page 2] INTERNET-DRAFT SGML Open Catalogs and MIME 2/21/96 1. Introduction.................................................4 1.1 Overview....................................................4 2. Catalog Description..........................................5 2.1 Resolving System Identifiers................................5 2.2 Catalog Keywords............................................6 2.2.1 NOTATION..................................................7 2.2.2 SEMANTICS.................................................8 2.2.3 BASE......................................................8 2.2.4 OVERRIDE..................................................9 2.2.5 ENCODING..................................................9 2.2.6 MAPSOI...................................................10 2.2.7 User-Defined Keywords....................................10 2.3 Storage Object Identifiers.................................11 2.3.1 URLs as SOIs.............................................11 2.3.2 The Content-ID SOI.......................................11 3. Catalog Syntax..............................................11 4. Usage Guidelines............................................13 5. Examples....................................................14 5.1 Sending Only A Catalog.....................................14 5.1.1 MIME Message Content.....................................15 5.2 Sending a Catalog and a Document Entity....................15 5.2.1 MIME Message Content.....................................16 5.3 Sending a Catalog and All Document Components..............17 5.3.1 MIME Message Content.....................................17 5.4 Sending a Catalog for a Non-Document Entity................19 6. Security Considerations.....................................20 7. Acknowledgments.............................................20 8. References..................................................21 9. Authors' Address............................................21 Appendix A: SGML declaration Used In The Examples..............22 Appendix B: DTD Used In The Examples...........................24 Appendix C: SGML document Used In The Examples.................25 Appendix D: NOTATIONS..........................................27 Stinchfield [Page 3] INTERNET-DRAFT SGML Open Catalogs and MIME 2/21/96 1. Introduction This proposal describes how SGML Open catalogs and MIME mechanisms are used to exchange SGML documents on the World Wide Web, or via email. Using the extension mechanism provided by Technical Resolution 9401:1995 (TR9401) [10]- TR9401 contains the technical description of SGML Open catalogs - this proposal describes new catalog keywords required for SGML document interchange. In addition, Uniform Resource Locators (URL) [8] are used to allow greater flexibility in the addressing of storage objects. This flexibility is intended to allow addressing of storage objects encapsulated in MIME messages, or addressable via the World Wide Web. A MIME body part containing an SGML Open catalog is tagged with the content type "application/sgml-open- catalog" [5]. Some benefits to using SGML Open catalogs to interchange SGML documents are: o a client only needs a catalog to begin processing, it simply fetches the components referenced in the catalog as they are needed; o a client that understands catalogs has a way to fetch components of a document that it doesn't already have; o document components do not have to be modified in order to be referenced in a catalog; o components of a document can be distributed across many servers; o catalogs do not depend on MIME, therefore, they can be used in other packaging schemes; o the impact on MIME is minimized; o catalogs are an implemented, proven, and widely used technology; o a document's system identifiers can be referenced in a catalog and subsequently resolved by a client. 1.1 Overview TR9401 defined catalog-keywords identify SGML document components, such as an SGML Declaration, a DTD, or a document entity. Catalogs containing only TR9401 catalog-keywords are useful for sharing documents between applications on a single system. These same catalogs are less useful for sharing documents between applications on remote and heterogeneous systems. For example, a system identifier that describes an absolute path to an MS-DOS file is useful on a PC but is not likely to be very useful on a UNIX system. Using the extension mechanism of TR9401, this proposal defines new catalog-keywords needed to address this problem, and others that are encountered when attempting to interchanging SGML documents over the World Wide Web, or via email. Stinchfield [Page 4] INTERNET-DRAFT SGML Open Catalogs and MIME 2/21/96 The new keywords described in this proposal include: NOTATION, BASE, SEMANTICS, OVERRIDE, MAPSOI, and ENCODING. NOTATION is used to describe a document's SGML NOTATION declaration [3][11]. OVERRIDE indicates the TR9401 processing mode[10] for resolving external identifiers. BASE defines an absolute URL and is used for resolving relative URLs found in the catalog. SEMANTICS is used to reference semantic processing information such as stylesheets. MAPSOI provides a mapping between system identifiers and is useful for exchanging documents with SGML systems that are not catalog aware. ENCODING describes the encoding of catalog entries; it is possible for each catalog entry to have its own encoding. In addition to catalog keywords, this proposal describes a system- independent SOI to be either a URL, a relative URL, or a MIME Content-ID. The usefulness of URLs and relative URLs is evident from World Wide Web. A Content-ID SOI identifies a document component contained in a MIME body part [13]. Typically, a Content-ID SOI describes the location of a document component within the same multipart message as the catalog. 2. Catalog Description A catalog contains zero or more catalog entries. Each entry consists of a keyword, zero or more keyword attributes, and, usually, a storage object identifier defined as a URL, a relative URL, or a Content-ID. Relative URLs are resolved using the value of the BASE catalog entry. When no BASE entry exists relative URLs are resolved with respect to the location of the catalog. 2.1 Resolving System Identifiers An SGML system identifier contains system-specific information used for locating an entity: a filename is an example of system-specific information. The kinds of system identifiers supported by an SGML system depends on the capabilities of its entity manager. Usually, there are two entity managers involved in a document exchange - in this document one of the entity managers is referred to as the sender's entity manager, and the other is referred to as the receiver's entity manager. Typically, the capabilities of the sender's entity manager is different from that of the receiver's, and the sender is usually unaware of the receiver's capabilities. The OVERRIDE and MAPSOI keywords are used to solve this problem. (Note, sometimes, especially for legacy SGML systems, this problem can only be solved by rewriting the document's system identifiers. Algorithms for rewriting system identifiers are beyond the scope of this document.) Stinchfield [Page 5] INTERNET-DRAFT SGML Open Catalogs and MIME 2/21/96 Setting the OVERRIDE keyword to "YES" directs the receiving system to use the catalog to re-map system identifiers occurring in the document. For example, the following is an entity declaration with a system identifier of "defc1.sgm": When a server creates a multipart message containing entity "c1" and a catalog that references it, the catalog entry for "c1" would look like this: OVERRIDE "YES" ENTITY "c1" "Content-ID:<==toons==>" A receiving SGML system that understands SGML Open catalogs, the extensions proposed in this document, and MIME can simply process the catalog. It is likely that multipart messages received over the World Wide Web will be processed this way. For email, the MUA will likely save the body part defined by "Content-ID:<==toons==>" to a file, and a helper application will rewrite the catalog to reflect the new location of "c1": OVERRIDE "YES" ENTITY "c1" "c:\tmp\blurt.it" It is useful for the helper application to save the body part using the original SOI of "c1". Doing so, for this example, would relieve the receiver's SGML system from having to process the catalog. The MAPSOI keyword facilitates this. For example, the aforementioned catalog contained in the multipart message can be rewritten to look like this: OVERRIDE "YES" ENTITY "c1" "Content-ID:<==toons==>" MAPSOI "defc1.sgm" "Content-ID:<==toons==>" The contents of the entity named "c1" are found in "Content- ID:<==toons==>". The original system identifier for "Content- ID:<==toons==>" is "defc1.sgm". The receiver's helper application can use this information to save the entity using the original SOI, defc1.sgm, defined for it in the document. 2.2 Catalog Keywords A catalog contains entries for SGML document components. The order of the entries is important for the OVERRIDE, ENCODING, and BASE keywords. All entries are optional. A catalog can contain multiple entries with the same keyword. The following keywords are defined in TR9401 [10]: SGMLDECL - SGML declaration DOCUMENT - SGML document entity Stinchfield [Page 6] INTERNET-DRAFT SGML Open Catalogs and MIME 2/21/96 DOCTYPE - Document type declaration (DTD) LINKTYPE - link type name PUBLIC - public external identifier DTDDECL - SGML declaration plus public identifier meant to match a public identifier given as part of the doctype declaration to reference the external subset. ENTITY - entity name The following keywords are defined in this document using the grammar notation of TR9401: NOTATION - notation name SEMANTICS - name and type of the semantic information BASE - base URL OVERRIDE - defines which TR9401 processing mode to use ENCODING - character encoding MAPSOI - maps a system identifier from a document to a system identifier in the catalog X- - user-define keyword prefix 2.2.1 NOTATION The NOTATION catalog keyword refers to data content notations defined or referenced in a document. The syntax for NOTATION is: notation = ("NOTATION", ps+, notation_name, (ps+, storage_object_identifier)? ) The storage object identifier is optional for NOTATION. The following example illustrates how NOTATION could be used for Java scripts: input to JuggleBalls script, for example: specify number of items and juggling style. A catalog entry for the NOTATION declaration described above would look like: NOTATION "JuggleBalls" "http://www.bill.com/juggleballs.java" The processing of notations is system dependent- there's no way for a server to guarantee that a client can process a specific notation. The NOTATION keyword in the catalog may only give a hint, possibly a Stinchfield [Page 7] INTERNET-DRAFT SGML Open Catalogs and MIME 2/21/96 pointer, to a notation processor. It can be dangerous for the client to resolve a reference to a notation processor- loading and running a notation processor received from a remote, and potentially unsecured, site is dangerous. However, in a secure environment, exchanging scripts may be perfectly safe. See appendix D for some examples of some notations. 2.2.2 SEMANTICS There may be semantic information such as stylesheets associated with a document. Semantic information is not required for parsing the document and can be ignored by the client. However, it is often desirable for a client to access appropriate semantic specifications. The syntax for the SEMANTICS keyword is: semantics = ("SEMANTICS", ps+, semantic name, ps+, semantic type, ps+, semantic title, ps+, storage object identifier) Here are two examples: SEMANTICS "large-print" "DSSSL" "Wicked Large Print" "http://www.bill.com/style/large.sty" SEMANTICS "toc" "DSSSL" "Table of Contents" "toc.sty" 2.2.3 BASE SOIs may be relative. Relative SOIs can be resolved using a BASE keyword catalog entry. (Relative URLs and their resolution are discussed in [4].) There can be more than one BASE keyword in a catalog. Relative URLs are resolved with respect to the closest previously specified BASE keyword, an example follows the syntax definition. If no BASE entry applies to a catalog entry, then the URL of the catalog is used for relative URL resolution. The syntax for the BASE keyword is: base = ("BASE", ps+, storage_object_identifier) Here's an example of how BASE is used: ENTITY "Legal" "legal.sgm" BASE "http://www.bill.com/docs/memo/mine/" ENTITY "MyEnding" " ending.sgml" Stinchfield [Page 8] INTERNET-DRAFT SGML Open Catalogs and MIME 2/21/96 The entity "Legal" is resolved relative to the URL of the catalog. The absolute URL for entity "MyEnding" is "http://www.bill.com/docs/memo/mine/ending.sgml". 2.2.4 OVERRIDE The OVERRIDE keyword defines which TR9401 processing mode the SGML system's entity manager will use to resolve external identifiers. When OVERRIDE is "YES" the entity manager uses the catalog to resolve external identifiers, whether or not there is a system identifier defined for it in the document. When OVERRIDE is "NO" the entity manager uses the system identifiers found in the document when resolving references to external identifiers. The value of OVERRIDE is "NO" at the beginning of the catalog. There can be more than one OVERRIDE keyword in a catalog. The OVERRIDE value that applies to an entry is the closest previously specified one. The syntax for the OVERRIDE keyword is: override = ("OVERRIDE", ps+, mode) mode = (LIT, "YES",LIT) | (LITA,"YES",LITA) | (LIT, "NO", LIT) | (LITA,"NO", LITA) Here's an example: ENTITY "Legal" "legal.sgm" OVERRIDE "YES" ENTITY "MyEnding" " ending.sgml" For this example override is "NO" for the entity "Legal" and "YES" for the entity "MyEnding". 2.2.5 ENCODING The ENCODING keyword provides a way to include entities in different encodings within a single document. The syntax of the ENCODING keyword is: encoding = ( "ENCODING", ps+, encode_spec ) The ENCODING keyword indicates the encoding of catalog entries that follow. There can be more than one ENCODING entry in a catalog. When an ENCODING entry is found it supersedes the value of any preceding ENCODING entry. Stinchfield [Page 9] INTERNET-DRAFT SGML Open Catalogs and MIME 2/21/96 ISO-646 [17] is the default when no ENCODING keyword is specified. ISO-646 was selected as the default value because of the special role it plays in SGML: ISO-646 is the syntax-reference character set of the reference concrete syntax [3], pg 476. For example, the following catalog describes catalog entries, each with a different encoding: ENCODING "SHIFT-JIS" DOCUMENT "http://www.goeast.com/anaxi.sgm" ENCODING "ISO-10646-UTF7" DOCTYPE "MEMO" "http://www.gowest.com/dtds/memo.dtd" ENCODING "SHIFT-JIS" ENTITY "MyEnding" "http://www.goeast.com/ending.sgml" ENTITY "Legal" "http://www.goeast.com/company/legal.sgm" The document entity and the entities MyEnding and Legal are encoded in SHIFT-JIS while the DTD is encoded in ISO-10646-UTF7. 2.2.6 MAPSOI The MAPSOI keyword is used to map an original system identifier found in a document to the SOI used for it in the catalog. The MAPSOI keyword is similar to the SYSTEM keyword used by nsgmls [16]. The syntax for the MAPSOI keyword is: mapsoi = ("MAPSOI", original_soi, effective_soi ) For an example of how MAPSOI is used refer to the previous section entitled "Resolving System Identifiers". 2.2.7 User-Defined Keywords It is strongly recommended that user-defined keywords begin with "X-". This allows the catalog-parser to easily determine if a keyword is a user-defined keyword. Stinchfield [Page 10] INTERNET-DRAFT SGML Open Catalogs and MIME 2/21/96 2.3 Storage Object Identifiers Three types of SOIs are defined in this section. The first defines an SOI in terms of URLs. The second defines an SOI in terms of a MIME Content-ID. And the last defines an SOI using TR9401's definition of an SOI. The syntax for an SOI is: storage object identifier = url object identifier | content id object identifier | TR9401 storage object identifier 2.3.1 URLs as SOIs An SOI can be a URL [8] or a relative URL [4]. The SOI will need to be parsed to determine the SOI type. 2.3.2 The Content-ID SOI A Content-ID SOI specifies a MIME message body part. Note, the Content-ID SOI is expected to be replaced in the future with the cid URL [8]. The syntax for Content-ID based SOI is: content id object identifier = "Content-ID" ":" msg-id ; as defined in RFC 1521 [13] msg-id = as defined in RFC 822 [15] 3. Catalog Syntax catalog = ( ps*, ( (catalog_entry | user_defined), ps+ )* ) catalog_entry = TR9401:1995_keywords | notation | semantics | base | override | mapsoi | encoding TR9401:1995_keywords = refer to TR9401 [10] for a description of keywords for sgmldecl, document, doctype, public, entity, and linktype Stinchfield [Page 11] INTERNET-DRAFT SGML Open Catalogs and MIME 2/21/96 notation = ("NOTATION", ps+, notation_name, (ps+, storage_object_identifier)? ) notation_name = entity_name_spec entity_name_spec = as defined in TR9401 [10] semantics = ("SEMANTICS", ps+, semantic_name, ps+, semantic_type, ps+, semantic_title, ps+, storage_object_identifier) semantic_name = entity_name_spec semantic_type = entity_name_spec semantic_title = entity_name_spec base = ("BASE", ps+, storage_object_identifier) override = ("OVERRIDE", ps+, mode) mode = (LIT, "YES",LIT) | (LITA, "YES",LITA) | (LIT, "NO", LIT) | (LITA, "NO", LITA) encoding = ( "ENCODING" , ps+, encode_spec ) encode_spec = entity_name_spec mapsoi = ("MAPSOI", ps+, original_soi, ps+, effective_soi ) original_soi = storage_object_identifier effective_soi = storage_object_identifier user_defined = ("X-", keyword) Stinchfield [Page 12] INTERNET-DRAFT SGML Open Catalogs and MIME 2/21/96 storage_object_identifier = url_object_identifier | content_id_object_identifier | TR9401_storage_object_identifier url_object_identifier = as defined in RFC 1738[8] content_id_object_identifier = "Content-ID" ":" msg-id msg-id = as defined in RFC 822 [15] TR9401_storage_object_identifier = "storage object identifier" as defined in TR9401 [10] keyword = as defined by TR9401 ps = as defined in TR9401 [10] 4. Usage Guidelines There are some ambiguities in TR9401 which can be easily avoided by adhering to these guidelines: quote all keyword-attributes using either single or double quotes. This allows the parser to determine what is an attribute, and what is not, following a user-defined keyword; surround comments with whitespace. In other words, don't start a comment just after a token, doing so can lead to parsing ambiguities. Stinchfield [Page 13] INTERNET-DRAFT SGML Open Catalogs and MIME 2/21/96 5. Examples The SGML document used in all the examples is composed of the following components: o an SGML declaration, defined in Appendix A; o a Document type declaration (DTD), defined in Appendix B; o an SGML document entity, defined in Appendix C; o two SGML entities, defined in Appendix C; o a figure entity, not defined in this draft. In all examples the components of this SGML document are spread across multiple servers, except for the example entitled "Sending a Catalog and All of its Components". Each example defines its own unique catalog. The catalog varies from example to example depending on the number of document components sent along with it. The sender decides how many components to include in the MIME message. A document component that is not included in the MIME message can be resolved in one of two ways: 1) the client requests the component from its cache, that is, the component had been fetched while processing a previous request, or 2) the client requests the component using SOI defined for it in the catalog. The definitions for the following external identifiers are not included in this document: formal public identifiers: ISO 646:1983//CHARSET International Reference Version (IRV)//ESC 2/5 4/0 ISO 8879:1986//ENTITIES Numeric and Special Graphic//EN system identifier: ../style/all.sty" - DSSSL style sheet 5.1 Sending Only A Catalog In this example only the catalog is sent to the client. When the client's SGML system is capable of handling SGML Open catalogs, along with the extensions proposed in this document, the catalog can be passed, without modification, to the client's SGML System. Some pre- processing may be required when the client's SGML system cannot handle these kinds of catalogs. For example, a catalog-aware SGML system that does not understand the keywords proposed in this documents or URLs would need pre-processor to do the following: 1. fetch all of the components referenced in the catalog, Stinchfield [Page 14] INTERNET-DRAFT SGML Open Catalogs and MIME 2/21/96 2. store the components locally, and 3. update the catalog to reflect the new locations. Here are some reasons for sending just the catalog: o the server might only store catalogs, that is, the server does not store any document components; o the client may have requested only the catalog. Perhaps the client wants to compare the contents of this catalog with the contents of a different catalog. Or maybe the client already has most, if not all, of the document's components cached; o the server may want to keep network traffic down by increasing the likelihood that the client will get a cache hit on catalog entries. 5.1.1 MIME Message Content MIME-Version: 1.0 Content-Type: Application/SGML-Catalog; charset=us-ascii SGMLDECL "http://www.ebt.com/decl/ebtsgml.dcl" OVERRIDE "YES" PUBLIC "ISO 646:1983//CHARSET International Reference Version (IRV)//ESC 2/5 4/0" "http://www.iso.ch/charset/6461983.cha" PUBLIC "ISO Registration Number 100//CHARSET ECMA-94 Right-hand Part of Latin Alphabet Nr.1//ESC 2/13 4/1" "http://www.iso.ch/charset/ecma94.cha" PUBLIC "-//EBT//CAPACITY CoolCaps 1.0//" "http://www.ebt.com/decl/coolcaps.cap" PUBLIC "-//EBT//SYNTAX SinSyn 0.1//" "http://www.ebt.com/decl/syntax/sinsyn.syn" BASE "http://www.bill.com/docs/memo/mine/" DOCUMENT "anaxi.sgm" DOCTYPE "MEMO" "../../dtds/memo.dtd" PUBLIC "ISO 8879:1986//ENTITIES Numeric and Special Graphic//EN" "http://www.wcs.com/usr/wcs/isonum.ent" ENTITY "%ISOnum" "http://www.wcs.com/usr/wcs/isonum.ent" ENTITY "MyEnding" "ending.sgml" ENTITY "Legal" "../company/legal.sgm" SEMANTICS "large-print" "DSSSL" "../style/all.sty" 5.2 Sending a Catalog and a Document Entity This example describes how to send a catalog and a document entity using a Multipart message. This is a likely scenario for Web-based browsers where simultaneous rendering and resolution of external Stinchfield [Page 15] INTERNET-DRAFT SGML Open Catalogs and MIME 2/21/96 identifiers are necessary. For this example the server assumes the client already has the SGML declaration, the DTD, and a stylesheet - if this is not the, the client can easily request them. The document entity will likely contain enough text for a browser to render meaningful text on the display device, but it won't include the many entities that the text may link to. These external objects, like figures, can be resolved by either the entity manager, while the application is rendering the text, or on user demand, as for hyperlinked information. 5.2.1 MIME Message Content MIME-Version: 1.0 Content-Type: Multipart/Mixed; boundary=let-go-of-my-leg; --let-go-of-my-leg Content-Type: Application/SGML-Catalog; charset=us-ascii SGMLDECL "http://www.ebt.com/decl/ebtsgml.dcl" OVERRIDE "YES" PUBLIC "ISO 646:1983//CHARSET International Reference Version (IRV)//ESC 2/5 4/0" "http://www.iso.ch/charset/6461983.cha" PUBLIC "ISO Registration Number 100//CHARSET ECMA-94 Right-hand Part of Latin Alphabet Nr.1//ESC 2/13 4/1" "http://www.iso.ch/charset/ecma94.cha" PUBLIC "-//EBT//CAPACITY CoolCaps 1.0//" "http://www.ebt.com/decl/coolcaps.cap" PUBLIC "-//EBT//SYNTAX SinSyn 0.1//" "http://www.ebt.com/decl/syntax/sinsyn.syn" BASE "http://www.bill.com/docs/memo/mine/" DOCUMENT "Content-ID:" DOCTYPE "MEMO" "../../dtds/memo.dtd" PUBLIC "ISO 8879:1986//ENTITIES Numeric and Special Graphic//EN" "http://www.wcs.com/usr/wcs/isonum.ent" ENTITY "%ISOnum" "http://www.wcs.com/usr/wcs/isonum.ent" ENTITY "MyEnding" "ending.sgml" ENTITY "Legal" "../company/legal.sgm" SEMANTICS "large-print" "DSSSL" "../style/all.sty" MAPSOI "anaix.sgm" "Content-ID:" --let-go-of-my-leg Content-Type: Application/SGML; charset=us-ascii Content-ID: Content-Disposition: attachment; filename="anaxi.sgm" include document entity from Appendix C --let-go-of-my-leg-- Stinchfield [Page 16] INTERNET-DRAFT SGML Open Catalogs and MIME 2/21/96 5.3 Sending a Catalog and All Document Components Sending a catalog and all of a document's components at once is done using a Multipart message. 5.3.1 MIME Message Content MIME-Version: 1.0 Content-Type: Multipart/Mixed; boundary=go-speed-racer --go-speed-racer Content-Type: Application/SGML-Catalog; charset=us-ascii SGMLDECL "Content-ID:" OVERRIDE "YES" PUBLIC "ISO 646:1983//CHARSET International Reference Version (IRV)//ESC 2/5 4/0" "Content-ID:" PUBLIC "ISO Registration Number 100//CHARSET ECMA-94 Right-hand Part of Latin Alphabet Nr.1//ESC 2/13 4/1" "Content-ID:" PUBLIC "-//EBT//CAPACITY CoolCaps 1.0//" "Content-ID:" PUBLIC "-//EBT//SYNTAX SinSyn 0.1//" "Content-ID:" DOCUMENT "Content-ID:" DOCTYPE "MEMO" "Content-ID:" PUBLIC "ISO 8879:1986//ENTITIES Numeric and Special Graphic//EN" "Content-ID:" ENTITY "%ISOnum" "Content-ID=" ENTITY "MyEnding" "Content-ID:" ENTITY "Legal" "Content-ID:" SEMANTICS "large-print" "DSSSL" "Content-ID:" MAPSOI "anaix.sgm" "Content-ID:" MAPSOI "/usr/wcs/dtd/memo.dtd" "Content-ID:" MAPSOI "/usr/des/ending.sgm" "Content-ID:" --go-speed-racer Content-Type:Application/SGML; charset=us-ascii Content-ID:"" description of SGML declaration from Appendix A is included here --go-speed-racer Content-Type:Application/SGML; charset=us-ascii Content-ID:"" ISO 646 character set definition included here Stinchfield [Page 17] INTERNET-DRAFT SGML Open Catalogs and MIME 2/21/96 --go-speed-racer Content-Type:Application/SGML; charset=us-ascii Content-ID:"" description of Capacity from Appendix A is included here --go-speed-racer Content-Type:Application/SGML; charset=us-ascii Content-ID:"" description of Syntax from Appendix A is included here --go-speed-racer Content-Type:Application/SGML; charset=us-ascii Content-ID:"" Contents of ISO Registration Number 100//CHARSET ECMA-94 Right-hand Part of Latin Alphabet Nr.1//ESC 2/13 4/1 included here --go-speed-racer Content-Type: Application/SGML; charset=us-ascii Content-ID: Content-Disposition: attachment; filename="anaxi.sgm" include Document entity as described in Appendix C --go-speed-racer Content-Type: Application/SGML; charset=us-ascii Content-ID: Content-Disposition: attachment; filename="memo.dtd" include DTD as described from Appendix B --go-speed-racer Content-Type: Application/SGML; charset=us-ascii Content-ID: ISO 8879:1986 Entity set included here --go-speed-racer Content-Type: Application/SGML; charset=us-ascii Content-ID: include entity set defined for %ISOnum --go-speed-racer Content-Type: Application/SGML; charset=us-ascii Content-ID: Content-Disposition: attachment; filename="ending.sgm" include entity MyEnding as described in Appendix C Stinchfield [Page 18] INTERNET-DRAFT SGML Open Catalogs and MIME 2/21/96 --go-speed-racer Content-Type: Application/SGML; charset=us-ascii Content-ID: include entity Legal as described in Appendix C --go-speed-racer Content-Type: Application/SGML; charset=us-ascii Content-ID: included here is a bunch of DSSSL-Lite --go-speed-racer-- 5.4 Sending a Catalog for a Non-Document Entity This example describes what a server might send in response to a request for a non-document entity. All of the previous examples assume that the original request was for a document entity. SGML documents can get very deep and contain a large number of external identifier references. Likewise, the complete catalog for a document could get very large: a "complete catalog" contains all of the external identifiers referenced in all of a document's entities. There is no need to send the complete. All that's needed are enough entries in the catalog for the client system to resolve references declared in the entity being transferred. For example, Appendix C.2 defines an entity called "Legal" which includes a reference to an entity called "MyEnding". A request for "Legal" would result in a Multipart/Related message that looks like this: MIME-Version: 1.0 Content-Type: Multipart/Mixed; boundary=let-go-of-my-leg --let-go-of-my-leg Content-Type: Application/SGML-Catalog; charset=us-ascii BASE "http://www.bill.com/docs/memo/mine/" OVERRIDE "YES" ENTITY "Legal" "Content-ID:" ENTITY "MyEnding" "ending.sgml" --let-go-of-my-leg Content-Type: Application/SGML; charset=us-ascii Content-ID: include entity "Legal" from Appendix C.2 --let-go-of-my-leg-- Stinchfield [Page 19] INTERNET-DRAFT SGML Open Catalogs and MIME 2/21/96 6. Security Considerations SGML documents, like other compound documents, may contain entities whose media-types present security concerns, e.g. Application/PostScript. Further, SGML may contain explicit processing instructions for a presentation or composition system; use of such instructions present concerns similar to those of Application/PostScript. The use of active media-types with Notation declarations can provide an opportunity for the sender to execute a script or other code on the recipient's machine. 7. Acknowledgments Thanks to Andre Alguero, Jeff Cutler-Stamm, Steve DeRose, Chris Maden, Gavin Nicol, and Bill Smith for helping me with the content and structure of this document. Thanks to Martin Bryan, James Clark, John Klensin, and Ed Levinson for the many discussions and debates that helped me to clarify, I hope, many of the ideas contained in this document. Thanks also to Wayne Wohler of IBM for his help on SGML declarations. Stinchfield [Page 20] INTERNET-DRAFT SGML Open Catalogs and MIME 2/21/96 8. References [1] Wayne Wohler, "SGML declarations", http://www.sil.org/sgml/wlw11.html [2] Eric van Herwijnen, "Practical SGML", Second Edition, Kluwer Academic Publishers, 1994, ISBN 0-7923-9434-8 [3] Charles F. Goldfarb, "The SGML Handbook", Oxford University Press, 1994, ISBN 0-19-853737-9 [4] R. Fielding, "Relative Uniform Resource Locators", RFC 1808, ftp://ds.internic.net/rfc/rfc1808.txt [5] P. Grosso, "The Application/SGML-Open-Catalog Content Type", RFC [6] Daniel W. Connolly, HTML 2.0 SGML declaration found at http://www.w3.org/hypertext/WWW/MarkUp/html-spec/html.decl [7] T. Berners-Lee, "Universal Resource Identifiers in WWW: A Unifying Syntax for the Expression of Names and Addresses of Objects on the Network as used in the World-Wide Web", RFC 1630 [8] T. Berners-Lee, L. Masinter, and M. McCahill, "Uniform Resource Locators (URL)", RFC 1738 [10] Paul Grosso, "Entity Management", SGML Open Technical Resolution 9401:1995 (Amendment 1 to TR9401), http://www.sgmlopen.org/sgml/docs/library/9401.htm [11] Charles F. Goldfarb, "Entity Management in SGML", 11/30/93 [12] Sollins, K. and Masinter, L., "Functional Requirements for Uniform Resource Names", RFC 1737 [13] N.Borenstein, "MIME (Multipurpose Internet Mail Extensions) Part One: Mechanisms for Specifying and Describing the Format of Internet Message Bodies", RFC 1521 [14] "ISO 8879:1986 Information processing - The and office systems - Standard Generalized Markup Language (SGML)", Geneva, 15 October 1986 [15] D. H. Crocker, "Standard for the Format of ARPA Internet Text Messages", RFC 822 [16] J. Clark "nsgmls- a validating sgml parser ", http://www.jclark.com/nsgmls.txt [17] ISO 646- ISO 7-bit coded character set for information interchange 9. Authors' Address Don Stinchfield Electronic Book Technologies, Inc. One Richmond Square Providence, RI 02906 (401) 421-9550 x280 des@ebt.com Stinchfield [Page 21] INTERNET-DRAFT SGML Open Catalogs and MIME 2/21/96 Appendix A: SGML declaration Used In The Examples This Appendix contains the definitions for the SGML declaration, for the CAPACITY parameter, and for the SYNTAX parameter. The SGML declaration is a modified version of the one used for HTML 2.0 [6] - I changed the CAPACITY and SYNTAX declarations so that they referenced public identifiers. The following external identifiers are reference in the SGML declaration: o BASESET "ISO 646:1983//CHARSET International Reference Version (IRV)//ESC 2/5 4/0" o BASESET "ISO Registration Number 100//CHARSET ECMA-94 Right-hand Part of Latin Alphabet Nr.1//ESC 2/13 4/1" o CAPACITY PUBLIC "-//EBT//CAPACITY CoolCaps 1.0//" o SYNTAX PUBLIC "-//EBT//SYNTAX SinSyn 0.1//" A.1 SGML declaration Stinchfield [Page 23] INTERNET-DRAFT SGML Open Catalogs and MIME 2/21/96 Appendix B: DTD Used In The Examples The DTD listed below is a modified version of the one found on page 33 of Eric van Herwijnen's book called "Practical SGML" [2]. The following external identifier is used in the DTD: The above definition is for a parameter entity and it contains both a public identifier and a system identifier. The examples have both in the catalog. B.1 DTD %ISOnum; Stinchfield [Page 24] INTERNET-DRAFT SGML Open Catalogs and MIME 2/21/96 Appendix C: SGML document Used In The Examples The SGML document defined in this appendix is broken up into 3 parts: an SGML document entity and two SGML Entities. The SGML document entity contains references to external identifiers in the DOCTYPE and ENTITY declarations: o This one contains both a public identifier and a system identifier: o This ENTITY declaration has system identifier and a system identifiers parameter: o This one specifies a system identifier without specifying a system identifier parameter (this is provided for in the SGML Standard for implementers that want to resolve System Identifiers from the entity name alone [3, p378]): C.1 SGML document entity ] > Anaximander Cool Papa Shad &Legal;

Yo Anax, you've got a bizarre name!

&MyEnding;

 Stinchfield [Page 25] INTERNET-DRAFT SGML Open Catalogs and MIME 2/21/96 C.2 Entity Named "Legal"

If you or anyone you know tries to read this email then you're in really big trouble!

You know this is the end of the document when you see &MyEnding;

C.3 Entity Named "MyEnding" Regards, Don Stinchfield [Page 26] INTERNET-DRAFT SGML Open Catalogs and MIME 2/21/96 Appendix D: NOTATIONS D.1 Useful Notations For Tcl I have taken the ISBN number from John K. Ousterhout's book "Tcl and the Tk Toolkit" to create a Formal Public Identifier: Stinchfield [Page 27]