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INTERNET-DRAFT EXPIRES JANUARY 1998 INTERNET-DRAFT Network Working Group R. Faith INTERNET-DRAFT U. North Carolina, Chapel Hill Category: Standards Track B. Martin Miranda Productions 1 July 1997 A Dictionary Server Protocol <draft-rfced-info-faith-00.txt> 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 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.'' 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). Authors' Note [[This document has not yet been submitted or accepted as an offi- cial RFC. Two independent server implementations have been com- pleted, one at dict://dict.miranda.org:2628 and the other at dict://proteus.cs.unc.edu:2628. This note should be deleted when this memo is assigned an RFC number.]] Abstract The Dictionary Server Protocol (DICT) is a TCP transaction based query/response protocol that allows a client to access dictionary definitions from a set of natural language dictionary databases. 1. Introduction For many years, the Internet community has relied on the "webster" protocol for access to natural language definitions. The webster protocol supports access to a single dictionary and (optionally) to a single thesaurus. In recent years, the number of publicly avail- able webster servers on the Internet has dramatically decreased. Fortunately, several freely-distributable dictionaries and lexicons have recently become available on the Internet. However, these freely-distributable databases are not accessible via a uniform interface, and are not accessible from a single site. They are often small and incomplete individually, but would collectively provide an interesting and useful database of English words. Exam- ples include the Jargon file [JARGON], the WordNet database Faith, Martin [Page 1] I/D Dictionary Server Protocol 1 July 1997 [WORDNET], MICRA's version of the 1913 Webster's Revised Unabridged Dictionary [WEB1913], and the Free Online Dictionary of Computing [FOLDOC]. Translating and non-English dictionaries are also becom- ing available (for example, the FOLDOC dictionary is being trans- lated into Spanish). The webster protocol is not suitable for providing access to a large number of separate dictionary databases, and extensions to the current webster protocol were not felt to be a clean solution to the dictionary database problem. The DICT protocol is designed to provide access to multiple databases. Word definitions can be requested, the word index can be searched (using an easily extended set of algorithms), informa- tion about the server can be provided (e.g., which index search strategies are supported, or which databases are available), and information about a database can be provided (e.g., copyright, citation, or distribution information). Further, the DICT protocol has hooks that can be used to restrict access to some or all of the databases. 1.1. Requirements In this document, we adopt the convention discussed in Section 1.3.2 of [RFC1122] of using the capitalized words MUST, REQUIRED, SHOULD, RECOMMENDED, MAY, and OPTIONAL to define the significance of each particular requirement specified in this document. In brief: "MUST" (or "REQUIRED") means that the item is an absolute requirement of the specification; "SHOULD" (or "RECOMMENDED") means there may exist valid reasons for ignoring this item, but the full implications should be understood before doing so; and "MAY" (or "OPTIONAL") means that his item is optional, and may be omitted without careful consideration. 2. Protocol Overview 2.1. Link Level The DICT protocol assumes a reliable data stream such as provided by TCP. When TCP is used, a DICT server listens on port 2628 (typ- ically, webster servers listened on port 2627). This server is only an interface between programs and the dictio- nary databases. It does not perform any user interaction or Faith, Martin [Page 2] I/D Dictionary Server Protocol 1 July 1997 presentation-level functions. 2.2. Lexical Tokens Commands and replies are composed of characters from the ISO-8859-1 character set [ISO]. More specifically, using the grammar conven- tions from [RFC822]: ; ( Octal, Decimal.) CHAR = <any ASCII character> ; ( 0-177, 0.-127.) CTL = <any ASCII control ; ( 0- 37, 0.- 31.) character and DEL> ; ( 177, 127.) CR = <ASCII CR, carriage return> ; ( 15, 13.) LF = <ASCII LF, linefeed> ; ( 12, 10.) SPACE = <ASCII SP, space> ; ( 40, 32.) HTAB = <ASCII HT, horizontal-tab> ; ( 11, 9.) <"> = <ASCII quote mark> ; ( 42, 34.) <'> = <ASCII single quote mark> ; ( 47, 39.) CRLF = CR LF WS = 1*(SPACE / HTAB) dqstring = <"> *(dqtext/quoted-pair) <"> dqtext = <any CHAR except <">, "\", and CTLs> sqstring = <'> *(dqtext/quoted-pair) <'> sqtext = <any CHAR except <'>, "\", and CTLs> quoted-pair = "\" CHAR atom = 1*<any CHAR except SPACE, CTLs, <'>, <">, and "\"> string = *<dqstring / sqstring / quoted-pair> word = *<atom / string> description = *<word / WS> text = *<word / WS> 2.3. Commands Commands consist of a command word followed by zero or more parame- ters. Commands with parameters must separate the parameters from each other and from the command by one or more space or tab charac- ters. Command lines must be complete with all required parameters, and may not contain more than one command. Each command line must be terminated by a CRLF. The grammar for commands is: Faith, Martin [Page 3] I/D Dictionary Server Protocol 1 July 1997 command = cmd-word *<WS cmd-param> cmd-word = atom cmd-param = database / strategy / word database = atom strategy = atom Commands are not case sensitive. Command lines MUST NOT exceed 1024 characters in length, counting all characters including spaces, separators, punctuation, and the trailing CRLF. There is no provision for the continuation of com- mand lines. 2.4. Responses Responses are of two kinds, status and textual. 2.4.1. Status Responses Status responses indicate the server's response to the last command received from the client. Status response lines begin with a 3 digit numeric code which is sufficient to distinguish all responses. Some of these may herald the subsequent transmission of text. The first digit of the response broadly indicates the success, failure, or progress of the previous command (based generally on [RFC640,RFC821]): 1yz - Positive Preliminary reply 2yz - Positive Completion reply 3yz - Positive Intermediate reply (not used by DICT) 4yz - Transient Negative Completion reply 5yz - Permanent Negative Completion reply The next digit in the code indicates the response category: Faith, Martin [Page 4] I/D Dictionary Server Protocol 1 July 1997 x0z - Syntax x1z - Information (e.g., help) x2z - Connections x3z - Authentication x4z - Unspecified as yet x5z - DICT System (These replies indicate the status of the receiver mail system vis-a-vis the requested transfer or other DICT system action.) x8z - Nonstandard (private implementation) extensions The exact response codes that should be expected from each command are detailed in the description of that command. Certain status responses contain parameters such as numbers and strings. The number and type of such parameters is fixed for each response code to simplify interpretation of the response. Other status responses do not require specific text identifiers. Parame- ter requirements are detailed in the description of relevant com- mands. Except for specifically detailed parameters, the text fol- lowing response codes is server-dependent. Parameters are separated from the numeric response code and from each other by a single space. All numeric parameters are decimal, and may have leading zeros. All string parameters MUST conform to the "atom" or "dqstring" grammar productions. If no parameters are present, and the server implementation pro- vides no implementation-specific text, then there MAY or MAY NOT be a space after the response code. Response codes not specified in this standard may be used for any installation-specific additional commands also not specified. These should be chosen to fit the pattern of x8z specified above. The use of unspecified response codes for standard commands is pro- hibited. 2.4.2. General Status Responses In response to every command, the following general status responses are possible: Faith, Martin [Page 5] I/D Dictionary Server Protocol 1 July 1997 500 Syntax error, command not recognized 501 Syntax error, illegal parameters 502 Command not implemented 503 Command parameter not implemented 420 Server temporarily unavailable 421 Server shutting down at operator request 2.4.3. Text Responses Before text is sent a numeric status response line, using a 1yz code, will be sent indicating text will follow. Text is sent as a series of successive lines of textual matter, each terminated with a CRLF. A single line containing only a period (decimal code 46, ".") is sent to indicate the end of the text (i.e., the server will send a CRLF at the end of the last line of text, a period, and another CRLF). If a line of original text contained a period as the first charac- ter of the line, that first period is doubled by the DICT server. Therefore, the client must examine the first character of each line received. Those that begin with two periods must have those two periods collapsed into one period. Those that contain only a sin- gle period followed by a CRLF indicate the end of the text response. Following a text response, a 2yz response code will be sent. Text lines MUST NOT exceed 1024 characters in length, counting all characters including spaces, separators, punctuation, the extra initial period (if needed), and the trailing CRLF. It is recommended that text use the US-ASCII [ASCII] or ISO-8859-1 [ISO] character sets, although it is currently beyond the scope of this standard to specify encoding for text. In the future, after significant experience with large databases in various languages has been gained, and after evaluating the need for character set and other encodings (e.g., compressed or BASE64 encoding), standard extensions to this protocol should be proposed. In the mean time, private extensions should be used to explore the parameter space to determine how best to implement these extensions. Faith, Martin [Page 6] I/D Dictionary Server Protocol 1 July 1997 3. Command and Response Details Below, each DICT command and appropriate responses are detailed. Each command is shown in upper case for clarity, but the DICT server is case-insensitive. Except for the AUTH command, every command described in this sec- tion MUST be implemented by all DICT servers. 3.1. Initial Connection When a client initially connects to a DICT server, a code 220 is sent if the client's IP is allowed to connect: 220 text msg-id The code 220 is a banner, usually containing host name and DICT server version information. The last sequence of characters in the banner is a msg-id, similar to the format specified in [RFC822]. The simplified description is given below: msg-id = "<" spec ">" ; Unique message id spec = local-part "@" domain local-part = msg-atom *("." msg-atom) domain = msg-atom *("." msg-atom) msg-atom = 1*<any CHAR except SPACE, CTLs, "<", ">", and "\"> Note that, in contrast to [RFC822], spaces and quoted pairs are not allowed in the msg-id. This restriction makes the msg-id much eas- ier for the client to locate and parse but does not significantly decrease any security benefits, since the msg-id may be arbitrarily long (as bounded by the response length limits set forth elsewhere in this document). This message id will be used by the client when formulating the authentication string used in the AUTH command. If the client's IP is not allowed to connect, then a code 530 is sent instead: 530 Access denied Faith, Martin [Page 7] I/D Dictionary Server Protocol 1 July 1997 Transient failure responses are also possible: 420 Server temporarily unavailable 421 Server shutting down at operator request For example, response code 420 should be used if the server cannot currently fork a server process (or cannot currently obtain other resources required to proceed with a usable connection), but expects to be able to fork or obtain these resources in the near future. Response code 421 should be used when the server has been shut down at operator request, or when conditions indicate that the ability to service more requests in the near future will be impossible. This may be used to allow a graceful operator-mediated temporary shutdown of a server, or to indicate that a well known server has been permanently removed from service (in which case, the text mes- sage might provide more information). 3.2. The DEFINE Command DEFINE database word 3.2.1. Description This command will look up the specified word in the specified database. All DICT servers MUST implement this command. If the database name is specified with an exclamation point (deci- mal code 33, "!"), then all of the databases will be searched until a match is found, and all matches in that database will be dis- played. If the database name is specified with a star (decimal code 42, "*"), then all of the matches in all available databases will be displayed. In both of these special cases, the databases will be searched in the same order as that printed by the "SHOW DB" command. If the word was not found, then status code 552 is sent. If the word was found, then status code 150 is sent, indicating that one or more definitions follow. For each definition, status code 151 is sent, followed by the tex- tual body of the definition. The first three space-delimited Faith, Martin [Page 8] I/D Dictionary Server Protocol 1 July 1997 parameters following status code 151 give the word retrieved, the name of the database (which is the same as the first column of the SHOW DB command), and a short description for the database (which is the same as the second column of the SHOW DB command). The short name is suitable for printing as: From name: before the definition is printed. This provides source information for the user. The textual body of each definition is terminated with a CRLF period CRLF sequence. After all of the definitions have been sent, status code 250 is sent. This command can provide optional timing information (which is server dependent and is not intended to be parsable by the client). This additional information is useful when debugging and tuning the server. 3.2.2. Responses 550 Invalid database, use "SHOW DB" for list of databases 552 No match 150 n definitions retrieved - definitions follow 151 word database name - text follows 250 ok (optional timing information here) Response codes 150 and 151 require special parameters as part of their text. The client can use these parameters to display infor- mation on the user's terminal. For code 150, parameters 1 indicates the number of definitions retrieved. For code 151, parameter 1 is the word retrieved, parameter 2 is the database name (the first name as shown by "SHOW DB") from which the definition has been retrieved, and parameter 3 is the the short database description (the second column of the "SHOW DB" command). Faith, Martin [Page 9] I/D Dictionary Server Protocol 1 July 1997 3.2.3. A Note on Virtual Datbases The ability to search all of the provided databases using a single command is given using the special "*" and "!" databases. However, sometimes, a client may want to search over some but not all of the databases that a particular server provides. One alter- native is for the client to use the SHOW DB command to obtain a list of databases and descriptions, and then (perhaps with the help of a human), select a subset of these databases for an interative search. Once this selection has been done once, the results can be saved, for example, in a client configuration file. Another alternative is for the server to provide "virtual" databases which merge several of the regular databases into one. For example, a virtual database may be provided which includes all of the translating dictionaries, but which does not include regular dictionaries or thesauri. The special "*" and "!" databases can be considered as names of virtual databases which provide access to all of the databases. If a server implements virtual databases, then the special "*" and "!" databases should probably exclude other virtual databases (since they merely provide information duplicated in other databases). If virtual databases are sup- ported, they should be listed as a regular database with the SHOW DB command (although, since "*" and "!" are required, they need not be listed). Virtual databases are an implementation-specific detail which has absolutely no impact on the DICT protocol. The DICT protocol views virtual and non-virtual databases the same way. We mention virtual databases here, however, because they solve a problem of database selection which could also have been solved by changes in the protocol. For example, each dictionary could be assigned attributes, and the protocol could be extended to specify searches over databases with certain attributes. However, this needlessly complicates the parsing and analysis that must be per- formed by the implementation. Further, unless the classification system is extremely general, there is a risk that it would restrict the types of databases that can be used with the DICT protocol (although the protocol has been designed with human-langauge databases in mind, it is applicable to any read-only database application, especially those with a single semi-unique alphanu- meric key and textual data). Faith, Martin [Page 10] I/D Dictionary Server Protocol 1 July 1997 3.3. The MATCH Command MATCH database strategy word 3.3.1. Description This command searches an index for the dictionary, and reports words which were found using a particular strategy. Not all strategies are useful for all dictionaries, and some dictionaries may support additional search strategies (e.g., reverse lookup). All DICT servers MUST implement the MATCH command, and MUST support the "exact" and "prefix" strategies. These are easy to implement and are generally the most useful. Other strategies are server dependent. The "exact" strategy matches a word exactly, although different servers may treat non-alphanumeric data differently. We have found that a case-insensitive comparison which ignores non-alphanumeric characters and which folds whitespace is useful for English- language dictionaries. Other comparisons may be more appropriate for other langauges or when using extended character sets. The "prefix" strategy is similar to "exact", except that it only compares the first part of the word. Different servers may implement these algorithms differently. The requirement is that strategies with the names "exact" and "prefix" exist so that a simple client can use them. Other strategies that might be considered by a server implementor are matches based on substring, suffix, regular expressions, soundex [KNUTH73], and Levenshtein [PZ85] algorithms. These last two are especially useful for correcting spelling errors. Other useful strategies perform some sort of "reverse" lookup (i.e., by searching definitions to find the word that the query suggests). If the database name is specified with an exclamation point (deci- mal code 33, "!"), then all of the databases will be searched until a match is found, and all matches in that database will be dis- played. If the database name is specified with a star (decimal code 42, "*"), then all of the matches in all available databases will be displayed. In both of these special cases, the databases will be searched in the same order as that printed by the "SHOW DB" command. If the strategy is specified using a period (decimal code 46, "."), then the word will be matched using a server-dependent default Faith, Martin [Page 11] I/D Dictionary Server Protocol 1 July 1997 strategy, which should be the best strategy available for interac- tive spell checking. This is usually a derivative of the Leven- shtein algorithm [PZ85]. If no matches are found in any of the searched databases, then sta- tus code 552 will be returned. Otherwise, status code 152 will be returned followed by a list of matched words, one per line, in the form: database word This makes the responses directly useful in a DEFINE command. The textual body of the match list is terminated with a CRLF period CRLF sequence. Following the list, status code 250 is sent, which may include server-specific timing and statistical information, as discussed in the section on the DEFINE command. 3.3.2. Responses 550 Invalid database, use "SHOW DB" for list of databases 551 Invalid strategy, use "SHOW STRAT" for a list of strategies 552 No match 152 n matches found - text follows 250 ok (optional timing information here) Response code 152 requires a special parameter as part of its text. Parameter 1 must be the number of matches retrieved. 3.4. The SHOW Command 3.4.1. SHOW DB SHOW DB SHOW DATABASES Faith, Martin [Page 12] I/D Dictionary Server Protocol 1 July 1997 3.4.1.1. Description Displays the list of currently accessible databases, one per line, in the form: database description The textual body of the database list is terminated with a CRLF period CRLF sequence. All DICT servers MUST implement this com- mand. Note that some databases may be restricted due to client domain or lack of user authentication (see the AUTH command). Information about these databases is not available until authentication is per- formed. Until that time, the client will interact with the server as if the additional databases did not exist. 3.4.1.2. Responses 110 n databases present - text follows 554 No databases present Response code 110 requires a special parameter. Parameter 1 must be the number of databases available to the user. 3.4.2. SHOW STRAT SHOW STRAT SHOW STRATEGIES 3.4.2.1. Description Displays the list of currently supported search strategies, one per line, in the form: strategy description The textual body of the strategy list is terminated with a CRLF period CRLF sequence. All DICT servers MUST implement this Faith, Martin [Page 13] I/D Dictionary Server Protocol 1 July 1997 command. 3.4.2.2. Responses 111 n strategies available - text follows 555 No strategies available Response code 111 requires a special parameter. Parameter 1 must be the number of strategies available. 3.4.3. SHOW INFO SHOW INFO database 3.4.3.1. Description Displays the source, copyright, and licensing information about the specified database. The information is free-form text and is suit- able for display to the user in the same manner as a definition. The textual body of the information is terminated with a CRLF period CRLF sequence. All DICT servers MUST implement this com- mand. 3.4.3.2. Responses 550 Invalid database, use "SHOW DB" for list of databases 112 database information follows These response codes require no special parameters. 3.4.4. SHOW SERVER SHOW SERVER 3.4.4.1. Description Displays local server information written by the local Faith, Martin [Page 14] I/D Dictionary Server Protocol 1 July 1997 administrator. This could include information about local databases or strategies, or administrative information such as who to contact for access to databases requiring authentication. All DICT servers MUST implement this command. 3.4.4.2. Responses 114 server information follows This response code requires no special parameters. 3.5. The CLIENT Command CLIENT text 3.5.1. Description This command allows the client to provide information about itself for possible logging and statistical purposes. All clients SHOULD send this command after connecting to the server. All DICT servers MUST implement this command (note, though, that the server doesn't have to do anything with the information provided by the client). 3.5.2. Responses 250 ok (optional timing information here) This response code requires no special parameters. 3.6. The STATUS Command STATUS 3.6.1. Description Display some server-specific timing or debugging information. This Faith, Martin [Page 15] I/D Dictionary Server Protocol 1 July 1997 information may be useful in debugging or tuning a DICT server. All DICT servers MUST implement this command (note, though, that the text part of the response is not specified and may be omitted). 3.6.2. Responses 210 (optional timing and statistical information here) This response code requires no special parameters. 3.7. The HELP Command HELP 3.7.1. Description Provides a short summary of commands that are understood by this implementation of the DICT server. The help text will be presented as a textual response, terminated by a single period on a line by itself. All DICT servers MUST implement this command. 3.7.2. Responses 113 help text follows This response code requires no special parameters. 3.8. The QUIT Command QUIT 3.8.1. Description This command is used by the client to cleanly exit the server. All DICT servers MUST implement this command. Faith, Martin [Page 16] I/D Dictionary Server Protocol 1 July 1997 3.8.2. Responses 221 Closing Connection This response code requires no special parameters. 3.9. The AUTH Command AUTH username authentication-string 3.9.1. Description The client can authenticate itself to the server using a username and password. The authentication-string will be computed as in the APOP protocol discussed in [RFC1939]. Briefly, the authentication- string is the MD5 checksum of the concatenation of the msg-id (obtained from the initial banner) and the "shared secret" that is stored in the server and client configuration files. Since the user does not have to type this shared secret when accessing the server, the shared secret can be an arbitrarily long passphrase. Because of the computational ease of computing the MD5 checksum, the shared secret should be significantly longer than a usual pass- word. Authentication may make more dictionary databases available for the current session. For example, there may be some publicly dis- tributable databases available to all users, and other private databases available only to authenticated users. Or, a server may require authentication from all users to minimize resource utiliza- tion on the server machine. Authentication is an optional server capability. The AUTH command MAY be implemented by a DICT server. 3.9.2. Responses 230 Authentication successful 531 Access denied, use "SHOW INFO" for server information These response codes require no special parameters. Faith, Martin [Page 17] I/D Dictionary Server Protocol 1 July 1997 4. Command Pipelining All DICT servers MUST be able to accept multiple commands in a sin- gle TCP send operation. Using a single TCP send operation for mul- tiple commands can improved DICT performance significantly, espe- cially in the face of high latency network links. The possible implementation problems for a DICT server which would prevent command pipelining are similar to the problems that prevent pipelining in an SMTP server. These problems are discussed in detail in [RFC1854], which should be consulted by all DICT server implementors. The main implication is that a DICT server implementation MUST NOT flush or otherwise lose the contents of the TCP input buffer under any circumstances whatsoever. A DICT client may pipeline several commands and must check the responses to each command individually. If the server has shut down, it is possible that all of the commands will not be pro- cessed. For example, a simple DICT client may pipeline a CLIENT, DEFINE, and QUIT command sequence as it is connecting to the server. If the server is shut down, the initial response code sent by the server may be 420 (temporarily unavailable) instead of 220 (banner). In this case, the definition cannot be retrieved, and the client should report and error or retry the command. If the server is working, it may be able to send back the banner, defini- tion, and termination message in a single TCP send operation. 5. URL Specification The DICT URL scheme is used to refer to definitions or word lists available using the DICT protocol: dict://<user>:<passphrase>@<host>:<port>/d:<word>:<database>:<n> dict://<user>:<passphrase>@<host>:<port>/m:<word>:<database>:<strat>:<n> The "/d" syntax specifies the DEFINE command (see section 3.2), whereas the "/m" specifies the MATCH command (section 3.3). Some or all of "<user>:<passphrase>@", ":<port>", "<database>", "<strat>", and "<n>" may be omitted. "<n>" will usually be omitted, but when included, it specifies the Faith, Martin [Page 18] I/D Dictionary Server Protocol 1 July 1997 nth definition or match of a word. A method for extracting exactly this information from the server is not avaiable using the DICT protocol. However, a client using the URL specification could obtain all of the definitions or matches, and then select the one that is specified. If "<user>:<passphrase>@" is omitted, no authentication is done. If ":<port>" is omitted, the default port (2628) SHOULD be used. If "<database>" is omitted, "!" SHOULD be used (see section 3.2.1). If "<strat>" is omitted, "." SHOULD be used (see section 3.3.1). Trailing colons may be omitted. For example, the following URLs might specify definitions or matches: dict://dict.org/d:shortcake: dict://dict.org/d:shortcake:* dict://dict.org/d:shortcake:wordnet: dict://dict.org/d:shortcake:wordnet:1 dict://dict.org/d:abcdefgh dict://dict.org/d:sun dict://dict.org/d:sun::1 dict://dict.org/m:sun dict://dict.org/m:sun::soundex dict://dict.org/m:sun:wordnet::1 dict://dict.org/m:sun::soundex:1 dict://dict.org/m:sun::: See [RFC1738] for the specification of Uniform Resource Locators. 6. Summary of Response Codes Below is a summary of response codes. A star (*) in the first col- umn indicates the response has defined arguments that must be pro- vided. Faith, Martin [Page 19] I/D Dictionary Server Protocol 1 July 1997 * 110 n databases present - text follows * 111 n strategies available - text follows 112 database information follows 113 help text follows 114 server information follows * 150 n definitions retrieved - definitions follow * 151 word database name - text follows * 152 n matches found - text follows 210 (optional timing and statistical information here) * 220 text msg-id 221 Closing Connection 230 Authentication successful 250 ok (optional timing information here) 420 Server temporarily unavailable 421 Server shutting down at operator request 500 Syntax error, command not recognized 501 Syntax error, illegal parameters 502 Command not implemented 503 Command parameter not implemented 530 Access denied 531 Access denied, use "SHOW INFO" for server information 550 Invalid database, use "SHOW DB" for list of databases 551 Invalid strategy, use "SHOW STRAT" for a list of strategies 552 No match 554 No databases present 555 No strategies available 7. Sample Conversations Theses are samples of the conversations that might be expected with a typical DICT server. The notation "C:" indicates commands set by the client, and "S:" indicates responses sent by the server. Blank lines are included for clarity and do not indicate actual newlines in the transaction. 7.1. Sample 1 - opening connection, HELP, DEFINE, and QUIT commands C: [ client initiates connection ] S: 220 dict.org dictd (version 0.9) <27831.860032493@dict.org> Faith, Martin [Page 20] I/D Dictionary Server Protocol 1 July 1997 C: HELP S: 113 Help text follows S: DEFINE database word look up word in database S: MATCH database strategy word match word in database using strategy S: [ more server-dependent help text ] S: . S: 250 Command complete C: DEFINE ! penguin S: 150 1 definitions found: list follows S: 151 "penguin" wn "WordNet 1.5" : definition text follows S: penguin S: 1. n: short-legged flightless birds of cold southern esp. Antarctic S: regions having webbed feet and wings modified as flippers S: . S: 250 Command complete C: DEFINE * shortcacke S: 150 2 definitions found: list follows S: 151 "shortcake" wn "WordNet 1.5" : text follows S: shortcake S: 1. n: very short biscuit spread with sweetened fruit and usu. S: whipped cream S: . S: 151 "Shortcake" web1913 "Webster's Dictionary (1913)" : text follows S: Shortcake S: \Short"cake`\, n. S: An unsweetened breakfast cake shortened with butter or lard, S: rolled thin, and baked. S: . S: 250 Command complete C: DEFINE abcdefgh S: 552 No match Faith, Martin [Page 21] I/D Dictionary Server Protocol 1 July 1997 C: quit S: 221 Closing connection 7.2. Sample 2 - SHOW commands, MATCH command C: SHOW DB S: 110 3 databases present: list follows S: wn "WordNet 1.5" S: foldoc "Free On-Line Dictionary of Computing" S: jargon "Hacker Jargon File" S: . S: 250 Command complete C: SHOW STRAT S: 111 5 strategies present: list follows S: exact "Match words exactly" S: prefix "Match word prefixes" S: substring "Match substrings anywhere in word" S: regex "Match using regular expressions" S: reverse "Match words given definition keywords" S: . S: 250 Command complete C: MATCH foldoc regex "s.si" S: 152 7 matches found: list follows S: foldoc Fast SCSI S: foldoc SCSI S: foldoc SCSI-1 S: foldoc SCSI-2 S: foldoc SCSI-3 S: foldoc Ultra-SCSI S: foldoc Wide SCSI S: . S: 250 Command complete Faith, Martin [Page 22] I/D Dictionary Server Protocol 1 July 1997 C: MATCH wn substring "abcdefgh" S: 552 No match 7.3. Sample 3 - Server downtime C: [ client initiates connection ] S: 420 Server temporarily unavailable C: [ client initiates connection ] S: 421 Server shutting down at operator request 7.4. Sample 4 - Authentication C: [ client initiates connection ] S: 220 dict.org dictd (version 0.9) <27831.860032493@dict.org> C: SHOW DB S: 110 1 database present: list follows S: free "Free database" S: . S: 250 Command complete C: AUTH joesmith authentication-string S: 230 Authentication successful Faith, Martin [Page 23] I/D Dictionary Server Protocol 1 July 1997 C: SHOW DB S: 110 2 databases present: list follows S: free "Free database" S: licensed "Local licensed database" S: . S: 250 Command complete 8. Security Considerations This document raises no security issues. 9. References [ASCII] US-ASCII. Coded Character Set - 7-Bit American Standard Code for Information Interchange. Standard ANSI X3.4-1986, ANSI, 1986. [FOLDOC] Howe, Denis, ed. The Free On-Line Dictionary of Comput- ing, <URL:http://wombat.doc.ic.ac.uk/> [ISO] ISO-8859. International Standard -- Information Processing -- 8-bit Single-Byte Coded Graphic Character Sets -- Part 1: Latin alphabet No. 1, ISO 8859-1:1987. [JARGON] The on-line hacker Jargon File, version 4.0.0, 25 JUL 1996, <URL:http://www.ccil.org/jargon/> [KNUTH73] Knuth, Donald E. "The Art of Computer Programming", Vol- ume 3: Sorting and Searching (Addison-Wesley Publishing Co., 1973, pages 391 and 392). Knuth notes that the soundex method was originally described by Margaret K. Odell and Robert C. Russell [US Patents 1261167 (1918) and 1435663 (1922)]. [PZ85] Pollock, Joseph J. and Zamora, Antonio, "Automatic spelling correction in scientific and scholarly text," CACM, 27(4): Apr. 1985, 358-368. Faith, Martin [Page 24] I/D Dictionary Server Protocol 1 July 1997 [RFC640] Postel, J., "Revised FTP Reply Codes", RFC-640, June, 1975. [RFC821] Postel, J., "Simple Mail Transfer Protocol", RFC-821, USC/Information Sciences Institute, August, 1982. [RFC822] Crocker, D., "Standard for the Format of ARPA Internet Text Messages", RFC-822, Department of Electrical Engineering, University of Delaware, August, 1982. [RFC977] Kantor, B., Lapsley, P., "Network News Transfer Protocol: A Proposed Standard for the Stream-Based Transmission of News", RFC-977, U.C. San Diego, U.C. Berkeley, February, 1986. [RFC1738] Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform Resource Locators (URL)", RFC-1738, CERN, Xerox PARC, Univer- sity of Minnesota, December 1994. [RFC1985] Freed, N., and Cargille, A., "SMTP Service Extension for Command Pipelining", RFC-1854, Innosoft International, Inc., and Network Working Group, October 1995. [RFC1939] Myers, J., Rose, M., "Post Office Protocol - Version 3", RFC-1939, Carnegie Mellon/Dover Beach Consulting, May, 1996. [RFC2068] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Bern- ers-Lee, T., "Hypertext Transfer Protocol -- HTTP/1.1", RFC-2068, U.C. Irvine, DEC, MIT/LCS, January, 1997. [WEB1913] Webster's Revised Unabridged Dictionary (G & C. Merriam Co., 1913, edited by Noah Porter). Online version prepared by MICRA, Inc., Plainfield, N.J. and edited by Patrick Cassidy <cassidy@micra.com>. For further information, see <URL:ftp://uiarchive.cso.uiuc.edu/pub/etext/gutenberg/etext96/pgw*>, and <URL:http://humanities.uchicago.edu/forms unrest/webster.form.html> [WORDNET] Miller, G.A. (1990), ed. WordNet: An On-Line Lexical Database. International Journal of Lexicography. Volume 3, Faith, Martin [Page 25] I/D Dictionary Server Protocol 1 July 1997 Number 4. <URL:http://www.cogsci.princeton.edu/~wn/> 10. Acknowledgements Thanks to Arnt Gulbrandsen and Nicolai Langfeldt for many helpful discussions. Thanks to Bennet Yee, Doug Hoffman, Kevin Martin, and Jay Kominek for extensive testing and feedback on the initial implementations of the DICT server. Thanks to Zhong Shao for advice and support. (Thanks to Brian Kanto, Phil Lapsley, and Jon Postel for writing exemplary RFCs which were consulted during the preparation of this document.) 11. Author's Addresses Rickard E. Faith EMail: faith@cs.unc.edu (or faith@acm.org) Bret Martin EMail: bamartin@miranda.org The majority of this work was completed while Bret Martin was a student at Yale University. Faith, Martin [Page 26] INTERNET-DRAFT EXPIRES JANUARY 1998 INTERNET-DRAFT