Internet-Draft: draft-kunze-thump-02.txt K. Gamiel THUMP Retrieval Protocol Renaissance Computing Inst. Expires 24 August 2007 J. Kunze University of California N. Nassar Etymon Systems 24 February 2007 THUMP -- The HTTP URL Mapping Protocol (http://www.ietf.org/internet-drafts/draft-kunze-thump-02.txt) Status of this Document By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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 obsoleted 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html Distribution of this document is unlimited. Please send comments to jak@ucop.edu Copyright (C) The IETF Trust (2007). All Rights Reserved. Abstract The HTTP URL Mapping Protocol (THUMP) is a set of URL-based conventions for retrieving information and conducting searches. THUMP can be used for focused retrievals or for broad database queries. A THUMP request is a URL containing a query string that starts with a `?', and can contain one or more THUMP commands. Returned records are formatted with kernel metadata as Electronic Resource Citations, which are similar to blocks of email headers. J. Kunze [Page 1]
Internet Draft THUMP Retrieval Protocol February 2007 1. Overview This document specifies The HTTP URL Mapping Protocol (THUMP), a set of URL-based conventions for retrieving information and conducting searches. THUMP can be used for focused retrievals; e.g., for a given known-item, asking that a specifically formatted subset of information about it be returned. It can also be used for broad database queries, such as finding all records matching the word, "monitor". A THUMP request is a URL containing a query string that starts with a `?', and can contain one or more THUMP commands. A request is passed to a server with HTTP GET (or POST if desired). The shortest request is a URL ending in `?', as in, http://example.foo.com/object321? which asks the server to return a metadata record describing the information item identified by the URL. This is a shorthand for the common request for a short description of a known-item; the completely spelled out equivalent in this case would be http://example.foo.com/object321?show(brief)as(anvl/erc) An example of a broad database search is, http://example.foo.com/?db(books)find(war and peace)show(full) Query strings and responses are UTF8-encoded [RFC3629]. A THUMP response is an HTTP message body containing one or more records. Records contain Kernel metadata [KERNEL] formatted as Electronic Resource Citations (ERC), which are similar to blocks of email headers. In an ERC each element consists of a label, colon, and value; long values are continued on indented lines and empty lines separate records. It will be possible in a future version of THUMP to request ERC records formatted in XML. 2. A Sample THUMP Session THUMP is very simple and follows the classical stateless HTTP communication model. This section contains a complete annotated example of a request and response exchange. To summarize, the requester sets up a TCP/HTTP session with the server system, sends a THUMP request inside an HTTP request, receives an answer inside an HTTP response, and closes the session. In the following example THUMP session, each line has been annotated to include a line number and whether it was the client or server that sent it. Without going into depth, the session has four pieces separated by blank lines: the client's piece (lines 1-3), the server's HTTP/THUMP response headers (4-7), and the body of the J. Kunze 2. Sample THUMP Session [Page 2]
Internet Draft THUMP Retrieval Protocol February 2007 server's response (8-18). The first and last lines (1 and 18) correspond to the client's steps to start the TCP session and the server's steps to end it, respectively. The heart of the request is the known-item metadata request indicated by the URL ending in a single `?' on line 2. 1 C: [opens session] C: GET http://ark.cdlib.org/ark:/13030/ft167nb0vq? HTTP/1.1 C: S: HTTP/1.1 200 OK 5 S: Content-Type: text/plain S: THUMP-Status: 0.5 200 OK S: S: set-start: California Digital Library | THUMP 0.5 | 20060606161407 S: | http://ark.cdlib.org/ark:/13030/ft167nb0vq? 10 S: | http://dublincore.org/groups/kernel/erc S: here: 1 | 1 | 1 S: S: erc: S: who: Stanton A. Glantz and Edith D. Balbach 15 S: what: Tobacco War: Inside the California Battles S: when: 20000510 S: where: http://ark.cdlib.org/ark:/13030/ft167nb0vq S: [closes session] The first two server response lines (4-5) above are typical with HTTP. The next line (6) is peculiar to THUMP, and indicates the THUMP version and a normal return status. The balance of the response consists of a record set header (lines 8-11) and a single metadata record (13-17) that comprises the service response. The record set header identifies (8-11) who created the set, what created it, when it was created, where an automated process can re- access the set, and where to look up the meaning of metadata elements; it ends in a line (11) whose respective sub-elements indicate that here in this communication the recipient can expect to find 1 record, starting at the record numbered 1, from a set consisting of a total of 1 record (i.e., here is the entire set, consisting of exactly one record). The returned record (13-17) is in the ERC format. It contains four elements that answer high priority questions regarding an expression of the object: who played a major role in expressing it, what the expression was called, when is was created, and where the expression may be found. 3. Keys and Citations A THUMP request is a command sequence operating on a Key, which is a base URL for a service point that supports THUMP. It is expected, J. Kunze 3. Keys and Citations [Page 3]
Internet Draft THUMP Retrieval Protocol February 2007 however, that the Key may generalize to service points in client- server computation contexts other than today's WWW. The Key uses a "citation-centered" system of reference. This means that data elements are addressed relative to an abstract object surrogate, or "citation". While some systems have stored metadata-based surrogates (e.g., library catalog records for books), many other systems do not. This is not an obstacle to using THUMP. The latter usually support the display or delivery of dynamically generated object citations, each consisting of such things as an access URL, a size, a date, a title, a snippet of relevant text (e.g., matching a query), plus links to related materials. Non-surrogate information objects in this model are, loosely speaking, the priority objects for end users, and include documents, articles, books, films, recordings, etc. Surrogates, whether static or dynamically generated, are important temporary stand-ins during discovery, filtering, and selection processes. They are easy to manipulate in large numbers because they are much more homogeneous than the objects they represent. Those objects are often too large, unwieldy, or rights-encumbered to be dealt with directly during discovery. Surrogates are also valuable in preservation since they can provide useful information about the original context, dependencies, and provenance of an object. 4. Key-Request Dualism Although THUMP does not specify anything about the structure of the Key, it is possible for a given Key string to express, often in an ad hoc manner, information similar to that expressed in the Request query string. The more intuitive the Key structure, the greater the chance for it to carry information that might appear to repeat or even contradict commands in the Request. For example, one server's conventions might consider http://example.foo.com/?db(books)find(war and peace)show(full) to be equivalent to http://example.foo.com/db=books/find=war+and+peace?show(full) There is a natural duality that servers may exploit by permitting or proposing (e.g., by returning) such semantically-laden Keys. Any conventions for re-expressing THUMP commands within the Key or for resolving apparent contradictions, however, are up to individual servers and are out of scope for this document. J. Kunze 4. Key-Request Dualism [Page 4]
Internet Draft THUMP Retrieval Protocol February 2007 This document recognizes the duality but does not constrain it except to say that for a given Key, a server that declares THUMP support MUST respond to the "help" command by listing all the commands (methods) valid for that Key. As a foundation requirement, the "help" command is a common way to ping a THUMP server to see if it is alive. At one extreme of the duality, when the request is completely absent (no `?' at all), a service may return a THUMP response. This might make sense for an entire service or only for certain specific Keys. There are cases when a server may wish to generate a temporary Key as a stand-in for a long or complex request and return it along with a subset of found records. For example, the request, http://example.foo.com/?db(books)find(war and peace)list(10|1) might return the first 10 records along with a Key that could be used in subsequent requests to return the next 10 records: http://example.foo.com/req98765?list(10|11) Note that this document makes no assumption about the dynamicity of queries, whether expressed partially or entirely in the Key or in the request. In either form, returned records might come from cached results or from results freshly computed upon each access. THUMP support does not constrain servers in this regard. 5. Request Summary There are several request forms described below, with output formats listed in a later section. Spaces have been inserted for readability in the forms below; usually, inter-command spaces would not be present. It is normal to formulate THUMP queries using only a subset of the commands specified. With a few important exceptions, this document is silent on how servers supply defaults or whether they signal errors for missing commands. All default actions and server- side request modifications SHOULD be reported back to the client. 5.1. Key ? help This form is required. A server that declares THUMP support MUST respond to the "help" command by listing all the commands (methods) valid for that Key. As a foundation requirement, the "help" command is a common way to ping a THUMP server to see if it is alive. 5.2. Key ? was(DESCRIPTION) when(DATE) resync This "metadata" command form provides nothing more than a way to carry a Key along with its description. The form is a "no-op" J. Kunze 5.2. ? was() when() resync [Page 5]
Internet Draft THUMP Retrieval Protocol February 2007 (except when "resync" is present) in the sense that the Key is treated as an adorned URL (as if no THUMP request were present). This form is designed as a passive data structrue that pairs a hyperlink with its metadata so that a formatted description might be surfaced by a client-side trigger event such as a "mouse-over". It is passive in the sense that selecting ("clicking on") the URL should result in ordinary access via the Key-as-pure-link as if no THUMP request were present. The form is effectively a metadata cache, and the DATE of last extraction tells how fresh it is. The "was" pseudo-command takes multiple arguments separated by "|", the first argument identifying the kind of DESCRIPTION that follows, e.g, was(erc|Tolstoy, L|War and Peace|1863|http://www.gutenberg.org/etext/2600) The "when" pseudo-command (optional) takes one argument that is the date that the immediately DESCRIPTION was extracted. The date, conforming to the [TEMPER] specification, looks like YYYYMMDDhhmmss. The "was" and "when" pseudo-commands can harmlessly accompany any THUMP request. The "resync" command, however, is a request to update the metadata. It returns a "metadata" form similar to the one submitted, but with refreshed metadata and no "resync" at the end. 5.3. Key ? in(DB) find(QUERY) list(RANGE) show(ELEMS) as(FORMAT) This form is used for generalized queries. The server is permitted to modify commands, such as by supplying missing commands (defaults), but SHOULD report the resulting filled-out command xxx. The "in" command specifies one or more database names separated by "|". If no "in" command is present, the server picks a suitable default database or returns an error. If no other commands are present, the server may treat the database as a result set or return an error. The "find" command specifies a QUERY that should produce a result set of matching records or an error. The result set is modeled as a numbered sequence of records that is returned "by reference" with a generated Key (see the "results" tag later) or as one or more returned subsequences of records, known as returned sets. If no "find" command is present, Key is expected to imply either a single record or a set of records. THUMP distinguishes between a result set and a returned set, which is a subsequence of the result set included in a given response. The QUERY consists of free text words separated by spaces. Reserved words begin with a ":" (colon), such as the :and, :or, and :not boolean operators. Parentheses can be used for grouping. Prepending J. Kunze 5.3. ? in() find() list() show() as() [Page 6]
Internet Draft THUMP Retrieval Protocol February 2007 "+" ("-") to a word is done when the requester desires that the word be present (absent) from search results. The double-quote character can be used to join words in a phrase or to turn off the special meanings of parentheses or ":+-" in front of words. The "list" command is used to request that a specific subsequence or RANGE of records be returned. The server should always use the starting point of the requested RANGE, but is free to return fewer records (or a partial record). In all cases the server must report what records or record fragment it has returned. If no "list" command is present, it is up to the server whether to return records, and if so, which records. RANGE is a pair of arguments, "LENGTH|START", indicating the number of records and starting record in the requested sequence. For example, a RANGE of "10I81" requests 10 records beginning with result set record 81. If both arguments are missing, as in "list()", it is considered a request for all records. If given as just "list(0)", it is a request that no records be returned directly, but a that the result set be returned by reference to a generated Key listed in the "results" tag of the returned set header. If LENGTH is positive and START is 0, the server should send LENGTH randomly selected result set records. If START is missing it defaults to 1; if LENGTH is missing, it is considered a request for all records starting from START. RANGE may also be used to request record fragments. A returned record set consists of either one or more entire (whole) records, or of exactly one fragment of one record. When a fragment is returned, the start position in the set header (described later) is indicated with S_F, where S is the record number and F is the fragment sequence number. To request the next fragment, a START is formulated by adding 1 to F. For example, "10|45_3" requests 10 records starting at fragment 3 of record 45 (only one fragment can be returned). The "show" command is used request that returned records be constituted with ELEMS elements. ELEMS is one or more element or element subset names separated by "|". Common element subset names are "brief", "full", and "support" (a record that is complete enough to show the server's commitment to the object. If no "show" command is present, it is up to the server which elements to return. The "as" command is used to request that returned records be formatted according to FORMAT. Common format names are "anvl/erc", "anvl/qdc", and "xml/marc". If no "as" command is present, the default format is usually "anvl/erc" (a plain text format that is eye-readable and machine-readable). J. Kunze 5.3. ? in() find() list() show() as() [Page 7]
Internet Draft THUMP Retrieval Protocol February 2007 5.4. Key ? This is a shorthand for Key ? show(brief) as(anvl/erc) which returns a brief object (identified by Key) description. Support for this shorthand is required. 5.5. Key ?? This is a shorthand for Key ? show(support) as(anvl/erc) which returns an object description full enough to contain the server provider's commitment statement. Support for this shorthand is required. 5.6. Key ? get() put() group() sort() apply() These commands are currently undefined and reserved by THUMP for future use. 6. Response Summary A THUMP response consists of a block of HTTP and extension headers, a blank line, and, if the THUMP-Status extension header was 200, a returned set of records. The Content-Type HTTP header is normally returned as Content-Type: text/plain so that the results will display correctly on a web browser's display. The THUMP content types "text/xml" and "text/html" are being considered. The rest of this section describes the THUMP extension headers and the structure of the returned record set. Extension headers are inserted in the block of HTTP response headers, usually near the end. Currently, one extension header, THUMP-Status, is defined, and it is required: THUMP-Status: THUMPVersion StatusCode ReasonPhrase It includes the version, a short human-readable phrase, and a 3-digit integer result code indicating the status of the attempt to execute the request. Defined StatusCodes and ReasonPhrases for THUMPVersion 0.5 are: J. Kunze 6. Response Summary [Page 8]
Internet Draft THUMP Retrieval Protocol February 2007 200: OK 400: Bad Request 402: Payment Required 403: Forbidden 404: Not Found 405: Method Not Allowed 408: Request Time-out If the status code other than 200, no record set should be sent. If the server wishes to convey any more detailed diagnostic or error information than may be expressed by the above status codes, it MUST set the code to 200 and use "error" or "warning" element tags within the returned record set. A blank line separates the HTTP response and THUMP-Status headers from the returned set that is the body of the response. The returned record set consists of a set-start header record followed by a sequence of records, each separated by one ore more blank lines, until end of stream (file) is reached. A set-end header record is optional. The format of the records is normally "anvl/erc", which specifies a serialization syntax [ANVL] with ERC semantics [KERNEL]. In a future version of THUMP it will be possible to request ERC semantics with "xml/erc". The next sections describe the special ANVL record used to introduce a record set and then the ERC records. 7. Returned Record Set Header What follows is a description of the anvl/erc returned record set encoding. The first record is a header record of the form, set-start: WHO_GENERATED | WHAT_SET | WHEN_GENERATED | WHERE_TO_RERUN | HOW_TO_INTERPRET here: NUM_RETURNED_SET | START_POSITION | NUM_RESULT_SET results: RESULT_SET_URI <optional> error: FATAL_ERROR_MESSAGE <optional> warning: CAUTIONARY_MESSAGE <optional> where the upper-cased tokens will be replaced by server-supplied values. Apart from the "set-start" element, which must appeart first, the other elements may appear in any order. Just as for an ordinary record, a blank line ends a set header record. The last three element tags are optional. If the "error" element is present, the supplied free-text message indicates a fatal error, and no usable returned records should be expected. If the "warning" element is present, the supplied message indicates a non-fatal error, and usable records may be returned. J. Kunze 7. Returned Record Set Header [Page 9]
Internet Draft THUMP Retrieval Protocol February 2007 7.1. "set-start" tag (required) The "set-start" element must be first in the record. Its associated values are: WHO_GENERATED The name or URI of the organization generating the set. WHAT_GENERATED The origin of the set, which might be simply "THUMP 0.5" or perhaps the name of an including collection or database. WHEN_GENERATED The date in [TEMPER] format when the set was generated. WHERE_TO_RERUN A URI containing a THUMP request that can be used to rerun the originating request (although it need not be a verbatim copy of the original request), and with differing results not unexpected in cases where the underlying collection is evolving. HOW_TO_INTERPRET The URI of a document defining the semantics of the element tags used in the returned record set. Note that for WHERE_TO_RERUN, the server may mirror the original THUMP request or may include a revision instead to indicate name remapping, defaults, interpretations, and corrections. An original request of find(vacuum tube)show(short) might come back "normalized", for example, as in find(vacuum%20tube)list(20|1)show(brief) 7.2. "here" tag (required) The "here" element is required, and has the form, here: NUM_RETURNED_SET | START_POSITION | NUM_RESULT_SET Its associated values are: NUM_RETURNED_SET The number of records in this returned set matching the request. A 0 (zero) indicates that no records were returned. If the result set is non-empty, the "results" tag may contain a URI that can be used as Key in subsequent THUMP requests. The special composite number, "0_1" indicates a set consisting of exactly one internal J. Kunze 7.2. [Page 10]
Internet Draft THUMP Retrieval Protocol February 2007 record fragment, with the final fragment indicated by "1_1". By concatenating all the fragments in the correct order, the client can reconstruct the whole record. START_POSITION The starting position of the first returned record relative to result set. If this number is 0 (zero), it indicates that the order of the returned records is undefined. If this number has the special composite form, "S_F", it indicates the record number S and sequence number F of the one record fragment in the returned set. The final fragment of a record is indicated when the server returns "1_1" for NUM_RETURNED_SET. Fragments should be requested in sequence by incrementing the sequence number, e.g., if 45_2 is returned (fragment 2 of record 45), the next fragment request from the client could be "list(10|45_3)", which request 10 records (the server unilaterally cuts this down to a single fragment) starting from fragment 3 of record 45. NUM_RESULT_SET The number of records in the result set. If this number is followed by a plus (e.g., 345+), it indicates that a minimum number that is still subject to growth. If followed by a tilda (e.g., 30000~), it indicates an approximate result set size. Examples of client/server exchanges that show how "list" commands might trigger server responses expressed in "here" returned set header tags. list(10|1) -> here: 10 | 1 | 27 list(10|11) -> here: 10 | 11 | 27 list(10|21) -> here: 7 | 21 | 27 list(20|1) -> here: 4 | 1 | 7 list(20|5) -> here: 0_1 | 5_1 | 7 list(20|5_2) -> here: 0_1 | 5_2 | 7 list(20|5_3) -> here: 1_1 | 5_3 | 7 list(20|6) -> here: 2 | 6 | 7 7.3. "results" tag (optional) The "results" element is optional, and has the form, results: RESULT_SET_URI Its associated value is a URI that can be used to refer to the results in a subsequent THUMP request, e.g., RESULT_SET_URI ? list(20|41) J. Kunze 7.3. [Page 11]
Internet Draft THUMP Retrieval Protocol February 2007 or Key ? find(:uri:RESULT_SET_URI :and parklands) 7.4. End of a record set The end of a record set is detected when the end of stream (or file) is encountered or, optionally, when a record beginning with the "set- end" element tag is encountered. This record has the form, set-end: OPTIONAL_COMMENT The OPTIONAL_COMMENT may contain arbitrary free text and may be absent. If a "set-end" is encountered, it is considered to close the most recently encountered "set-start". As usual, the record ends with a blank line. 8. Returned Records This section describes how a record in the sequence of returned records is encoded in the anvl/erc format. ANVL (A Name Value Language) defines the syntax and the ERC (Electronic Resource Citation) defines semantics. The URI for the ERC [KERNEL] reference should be included in the record set header. While a comprehensive description of the ERC record is out of scope for this document, some details are give below that may suffice for simple implementations. An ERC record is a sequence of tagged elements. It has the form, erc: who: WHO_EXPRESSED_THIS_ITEM what: WHAT_THE_EXPRESSION_WAS_CALLED when: WHEN_IT_WAS_EXPRESSED where: WHERE_THE_EXPRESSION_CAN_BE_FOUND how: DESCRIPTION_OR_SUMMARY_OF_ITEM <optional> why: COPYRIGHT_DISCLAIMER_AUDIENCE_STATEMENT <optional> note: ANY_TEXT <optional> ....... <any other tagged elements> <optional> The first five tagged elements are required. The required elements may be thought to answer questions about an "expression" of a resource (an item). All other elements are optional. The next ERC element shown above ("how") is concerned with the content of an item and the element after that ("why") with any high priority information that comes from the lawyerly domain -- the really hard questions. J. Kunze 8. Returned Records [Page 12]
Internet Draft THUMP Retrieval Protocol February 2007 A short form of the ERC is also possible that the above ordering for the first 6 elements. It has the form, erc: WHO | WHAT | WHEN | WHERE | HOW <optional> | WHY <optional> note: ANY_TEXT <optional> ....... <any other tagged elements> <optional> The line breaks among the first 6 elements are arbitrary. Together they are considered to be part of one long value for the "erc:" as long as they are continued on indented lines. In either form of the ERC, arbitrary additional elements are possible. 8.1. Empty values for required elements Although they are required, if no suitable element value can be found, a controlled code value for "empty" of the form (:ccode) should be used, drawing from the following reserved values: (:unkn) A null element term explaining that the value is unknown. Compared to :unav, this explanation carries a high degree of authority regarding the object described. Anonymous authorship is an example. (:unav) A null element term explaining that the value is unavailable indefinitely. Compared to :unkn, this explanation is intended for intermediary systems that know less about the object described and have to rely on the best metadata received. (:unac) A null element term explaining that the value is temporarily inaccessible. This might be due, for example, to a system outage. (:unap) A null element term explaining that the value is not applicable or makes no sense. (:unas) A null element term explaining that a value was never assigned. An untitled painting is an example. (:none) A null element term explaining that the element never had a value and never will. (:null) A null element term explaining that the value is explicitly empty. J. Kunze 8.1. Empty values for required elements [Page 13]
Internet Draft THUMP Retrieval Protocol February 2007 (:unal) A null element term explaining that the value is unallowed or suppressed intentionally. (:tba) A null element term explaining that the value is to be assigned or announced later. 9. FAQ -- Frequently Asked Questions 9.1. What's the difference between THUMP, OpenSearch, SRU/SRW, and OpenURL? All of these protocols are capable of expressing a parameter package on the right-hand side of a URL, and all of them reserve specific parameter names as having defined meanings. In theory, these packages can be extended arbitrarily to express any functionality with any level of complexity. There's no syntactic limitation to these protocols' expressiveness. The difference lies in how. THUMP uses a classic parenthesized argument list syntax while the others use the flat argument-value list syntax traditional on the web since 1995. OpenSearch and SRU/SRW are logical descendants of the complex Z39.50 search and retrieve protocol, but with restricted functionality and a text-based syntax. SRW and OpenURL define an XML-encoding for request parameters. OpenURL tends to be used for known-item linking. THUMP aims to be a more concise specification for key-based requests. 10. Appendix -- Motivation for Electronic Resource Citations (ERCs) An Electronic Resource Citation (or ERC, pronounced e-r-c) is a simple, compact, and printable record designed to hold data associated with an information resource. By design, the ERC is a metadata format that balances the needs for expressive power, very simple machine processing, and direct human manipulation. A founding principle of the ERC is that direct human contact with metadata will be a necessary and sufficient condition for the near term rapid development of metadata standards, systems, and services. Thus the machine-processable ERC format must only minimally strain people's ability to read, understand, change, and transmit ERCs without their relying on intermediation with specialized software tools. The basic ERC needs to be succinct, transparent, and trivially parseable by software. Borrowing from the data structuring format that underlies the successful spread of email and web services, the ERC format uses [ANVL], which is based on email and HTTP headers [RFC822]. There is a naturalness to ANVL's label-colon-value format (seen in the previous section) that barely needs explanation to a person beginning J. Kunze 10. Electronic Resource Citations (ERCs) [Page 14]
Internet Draft THUMP Retrieval Protocol February 2007 to enter ERC metadata. Besides simplicity of ERC system implementation and data entry mechanics, ERC semantics (what the record and its constituent parts mean) must also be easy to explain. ERC semantics are based on a reformulation and extension of the Dublin Core [DCORE] hypothesis, which suggests that the fifteen Dublin Core metadata elements have a key role to play in cross-domain resource description. The ERC design recognizes that the Dublin Core's primary contribution is the international, interdisciplinary consensus that identified fifteen semantic buckets (element categories), regardless of how they are labeled. The ERC then adds a definition for a record and some minimal compliance rules. In pursuing the limits of simplicity, the ERC design combines and relabels some Dublin Core buckets to isolate a tiny kernel (subset) of four elements for basic cross-domain resource description. For the cross-domain kernel, the ERC uses the four basic elements - who, what, when, and where - to pretend that every object in the universe can have a uniform minimal description. Each has a name or other identifier, a location, some responsible person or party, and a date. It doesn't matter what type of object it is, or whether one plans to read it, interact with it, smoke it, wear it, or navigate it. Of course, this approach is flawed because uniformity of description for some object types requires more semantic contortion and sacrifice than for others. That is why at the beginning of this document, the ARK was said to be suited to objects that accommodate reasonably regular electronic description. While insisting on uniformity at the most basic level provides powerful cross-domain leverage, the semantic sacrifice is great for many applications. So the ERC also permits a semantically rich and nuanced description to co-exist in a record along with a basic description. In that way both sophisticated and naive recipients of the record can extract the level of meaning from it that best suits their needs and abilities. Key to unlocking the richer description is a controlled vocabulary of ERC record types (not explained in this document) that permit knowledgeable recipients to apply defined sets of additional assumptions to the record. 10.1. ERC Syntax An ERC record is a sequence of metadata elements ending in a blank line. An element consists of a label, a colon, and an optional value. Here is an example of a record with five elements. J. Kunze 10.1. ERC Syntax [Page 15]
Internet Draft THUMP Retrieval Protocol February 2007 erc: who: Gibbon, Edward what: The Decline and Fall of the Roman Empire when: 1781 where: http://www.ccel.org/g/gibbon/decline/ A long value may be folded (continued) onto the next line by inserting a newline and indenting the next line. A value can be thus folded across multiple lines. Here are two example elements, each folded across four lines. who/created: University of California, San Francisco, AIDS Program at San Francisco General Hospital | University of California, San Francisco, Center for AIDS Prevention Studies what/Topic: Heart Attack | Heart Failure | Heart Diseases An element value folded across several lines is treated as if the lines were joined together on one long line. For example, the second element from the previous example is considered equivalent to what/Topic: Heart Attack | Heart Failure | Heart Diseases An element value may contain multiple values, each one separated from the next by a `|' (pipe) character. The element from the previous example contains three values. For annotation purposes, any line beginning with a `#' (hash) character is treated as if it were not present; this is a "comment" line (a feature not available in email or HTTP headers). For example, the following element is spread across four lines and contains two values: what/Topic: Heart Attack # | Heart Failure -- hold off until next review cycle | Heart Diseases 11. Security Considerations The THUMP protocol poses no direct risk to computers and networks. Implementors of THUMP services need to be aware of security issues when querying networks and filesystems, and the concomitant risks from spoofing and obtaining incorrect information. These risks are no greater for THUMP than for any other kind of HTTP-based application. For example, recipients of a URL with embedded THUMP commands should treat it like a URL and be aware that the identified J. Kunze 11. Security Considerations [Page 16]
Internet Draft THUMP Retrieval Protocol February 2007 service may no longer be operational. THUMP clients and servers subject themselves to all the risks that accompany normal operation of the protocols underlying mapping services (e.g., HTTP, Z39.50). As specializations of such protocols, a THUMP service may limit exposure to the usual risks. Indeed, THUMP services may enhance a kind of security by helping users identify long-term reliable references to information objects. 12. Authors' Addresses Kevin Gamiel Renaissance Computing Institute (RENCI) University of North Carolina at Chapel Hill Duke University North Carolina State University Fax: +1 919-445-9669 EMail: kgamiel@renci.org John A. Kunze California Digital Library University of California, Office of the President 415 20th St, 4th Floor Oakland, CA 94612-3550, USA Fax: +1 510-893-5212 EMail: jak@ucop.edu Nassib Nassar Etymon Systems P.O. Box 12484 Research Triangle Park, NC 27709, USA EMail: nassar@etymon.com 13. Informative References [ANVL] J. Kunze, B. Kahle, et al, "A Name-Value Language", work in progress, http://www.cdlib.org/inside/diglib/ark/anvlspec.pdf [ARK] J. Kunze, "Towards Electronic Persistence Using ARK Identifiers", Proceedings of the 3rd ECDL Workshop on Web Archives, August 2003, (PDF) http://bibnum.bnf.fr/ecdl/2003/proceedings.php?f=kunze [DCORE] Dublin Core Metadata Initiative, "DCMI Terms", December 2006, http://dublincore.org/documents/dcmi-terms/. J. Kunze 13. Informative References [Page 17]
Internet Draft THUMP Retrieval Protocol February 2007 [KERNEL] Dublin Kernel Metadata, work in progress within the Dublin Core Metadata Initiative (DCMI) Kernel Working Group, http://dublincore.org/groups/kernel/ [RFC822] D. Crocker, "Format of ARPA Internet Text Messages", August 1982, http://www.ietf.org/rfc/rfc822.txt [RFC3629] F. Yergeau, "UTF-8, a Transformation Format of ISO 10646", November 2003, http://www.ietf.org/rfc/rfc3629.txt 14. Copyright Notice Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Expires 24 August 2007 J. Kunze 14. Copyright Notice [Page 18]
Internet Draft THUMP Retrieval Protocol February 2007 Table of Contents Status of this Document . . . . . . . . . . . . . . . . . . . . . . 1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. A Sample THUMP Session . . . . . . . . . . . . . . . . . . . . . 2 3. Keys and Citations . . . . . . . . . . . . . . . . . . . . . . . 3 4. Key-Request Dualism . . . . . . . . . . . . . . . . . . . . . . 4 5. Request Summary . . . . . . . . . . . . . . . . . . . . . . . . 5 5.1. Key ? help . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5.2. Key ? was(DESCRIPTION) when(DATE) resync . . . . . . . . . . . 5 5.3. Key ? in(DB) find(QUERY) list(RANGE) show(ELEMS) as(FOR- MAT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.4. Key ? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 5.5. Key ?? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 5.6. Key ? get() put() group() sort() apply() . . . . . . . . . . . 8 6. Response Summary . . . . . . . . . . . . . . . . . . . . . . . . 8 7. Returned Record Set Header . . . . . . . . . . . . . . . . . . . 9 7.1. "set-start" tag (required) . . . . . . . . . . . . . . . . . . 10 7.2. "here" tag (required) . . . . . . . . . . . . . . . . . . . . 10 7.3. "results" tag (optional) . . . . . . . . . . . . . . . . . . . 11 7.4. End of a record set . . . . . . . . . . . . . . . . . . . . . 12 8. Returned Records . . . . . . . . . . . . . . . . . . . . . . . . 12 8.1. Empty values for required elements . . . . . . . . . . . . . . 13 9. FAQ -- Frequently Asked Questions . . . . . . . . . . . . . . . 14 9.1. What's the difference between THUMP, OpenSearch, SRU/SRW, and OpenURL? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 10. Appendix -- Motivation for Electronic Resource Citations (ERCs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 10.1. ERC Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 15 11. Security Considerations . . . . . . . . . . . . . . . . . . . . 16 12. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 17 13. Informative References . . . . . . . . . . . . . . . . . . . . 17 14. Copyright Notice . . . . . . . . . . . . . . . . . . . . . . . 18 J. Kunze 14. Copyright Notice [Page 2]