This file documents the Trivial Database Search Facility (TDBSF).

Copyright (c) 2001-2013 Florent Rougon.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with the Invariant Section being “GNU GENERAL PUBLIC LICENSE”, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation License”.

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This manual documents the TDBSF (version 3.2.2, 29 March 2013), a small search engine for “databases” stored in a very simple (trivial) format.

--- The Detailed Node Listing ---


Search expression syntax

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The TDBSF (Trivial Database Search Facility) is a small search engine for “databases” stored in a very simple (trivial) format.

The engine is written in Python and as of March 2009, there is only one really usable user interface, written in ELisp for Emacs. However, the TDBSF is designed to ease the addition of interfaces, so this is only a matter of whether there are people wanting to use it outside Emacs or not.

The databases that can be used with the TDBSF consist of a set of text files divided into records. Each record consists of four parts—a header, a body and two parts used to identify them: the beginning-of-header (boh) and the end-of-header (eoh).

The beginning of a header is identified by a regular expression (whose syntax is defined in the “re” module for the Python programming langage). Another regular expression is used to define where it ends and therefore where the body of the record begins. The body ends where the next beginning-of-header regular expression matches or at end of the file. For instance, a record could look like this (the last two lines belong to the second record):

     Header of the first record
     As many lines as necessary
     Header of the next record...

A TDBSF database file is a file containing one or more records like that in sequence.

The TDBSF tests a search expression on each record of a database defined by its set of database files and allows the user to view/edit (depending on the interface used) the matching records.

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I wrote this software because my father used during years an old shareware to retreive some data stored in “databases” as described above, which has severe limitations, is not easily extensible and only works on MS-DOS and some versions of MS Windows. The TDBSF enables him to solve these problems while keeping its “databases” unchanged. Besides, it is much more powerful and fast than the original tool.

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1 How to use the TDBSF

Supposing you have followed the instructions in the INSTALL file, here is what you have to do in order to use the TDBSF with the Emacs interface1:

  1. Type your search expression in an Emacs buffer of your choice and set the region (characters between the Emacs point and mark) around it (this can be done by selecting the expression with the left mouse button).

    A search expression consists of regular expressions combined with optional parentheses and the following operators: & (logical and), | (logical or), ! (logical not) and near expressions (for instance, foo ~4 bar ~2 baz ~3 quux is a near expression that matches if and only if ‘foo’ and ‘bar’ are found within—at most—4 words, this occurrence of ‘bar’ being found within 2 words of an occurrence of ‘baz’ itself found within 3 words of ‘quux’). Simple words and quoted groups of words "like this" are valid regular expressions. Example:

              swallow ~4 carry ~3 coconut & "air-speed velocity" & !European

    which is the same as:

              (swallow ~4 carry ~3 coconut) & "air-speed velocity" & (!European)

    By the way, such expressions would probably be more useful with flags making the regular expressions case-insensitive. See Search expression syntax, for more information.

    Note: after being successfully parsed, a search expression is converted into a tree and this tree is optimized in order to maximize the search speed for this expression. This is done by attributing a weight to each subexpression of the search expression (a regular expression will have a weight related to its length; for near expressions, the weights of its elements will be multiplied together; for & and | operators, the weights of the operands are added, etc.). Then, the order in which the operations are performed is chosen so that the “lighter” operations are more likely to be performed than the “heavier” ones (base idea: in an expression such as a & b & c, if a is false, then neither b nor c needs to be evaluated: the whole expression is false; similar considerations can be done with the | operator and with near expressions).

  2. Type M-x tdbsf which will ask you all the other info needed, namely:

The results are presented in a summary buffer named *TDBSF Results Summary* put in TDBSF Summary mode. There is one reference to a matching record per line, displaying the file name where it was found and the first line of its header. Just hit <RET> on a line in this buffer (or click with the middle button of the mouse) and another buffer will be popped, visiting the file and showing the record in TDBSF Database File mode, where some highlighting is done to show why the record matched2.

Sometimes, one can be surprised that not all matches of a regexp that is part of the search expression are highlighted in a matching record. This is expected, because the way search expressions are evaluated in each record is optimized for speed. For instance, suppose the search expression is "cat%I" | "donkey%I" | "turkey%I" and the search engine looks for matches of "cat%I" first (which is likely since it is the shortest of the three regular expressions). If such matches are found, the two other animals won't be searched for at all, much less highlighted, since it is logically sufficient that "cat%I" matches for the whole search expression to match. Moreover, if the search string is header or body (remember the four options) and the search expression matches the header of a given record, then the body of that record won't be searched at all, and therefore not highlighted in any way.

In TDBSF Summary mode, you can type C-c C-n or C-c C-p to jump to the next or previous matching record, respectively, visiting a new file if needed.

The following two paragraphs deal with details that can be skipped on the first reading of this manual.

Emacs markers are set in TDBSF Database File mode so that inserting or deleting text in the file will not cause any problem when jumping to the previous/next record or to any record of that file from the *TDBSF Results Summary* buffer. Also, the fontification is performed with overlays which also have markers to specify their beginning and end, therefore fontification doesn't get screwed in case of insertion/deletion in a buffer in TDBSF Database File mode.

Because of these mechanisms, TDBSF refuses to use a buffer (in order to display a record) if it is marked as modified. This is because information such as the positions where each record starts is stored into buffer-local variables when TDBSF performs a search and becomes outdated when buffers visiting TDBSF databse files are modified. If you edit a database file and want accurate jumps from the *TDBSF Results Summary* buffer to the modified buffer (through <RET> or middle click), the simplest way is to save the modified buffer and launch the search again.

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2 Search expression syntax

A search expression is an expression which can be checked against a string (e.g. the body of a record) to see if it matches that string or not.

It is a combination of simple elements that match or don't match the string, using the boolean and (&), or (|) and not (!) operators as well as parentheses to force the order in which the operations are performed (a match is considered as a boolean “true” and a non-match as a “false”). In the TDBSF terminology, the simplest of these elements are called atoms and are either regular expressions or near-expressions (near-expressions will be defined later).

Any whitespace (spaces, tabulations or newlines) between atoms and operators is ignored and can therefore be used to improve the readability of a search expression.

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2.1 Regular expressions in a TDBSF search expression

The regular expression syntax used by the TDBSF is that of the “re” module of the Python programming langage. As of February 2013, its documentation can be found directly at In any case, you will find it starting from This syntax is very powerful, therefore a bit complex and cannot be detailed here: it would result in a useless, bad duplicate.

There are two ways to embed a re-module-style regular expression (regexp) in a TDBSF search expression:

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2.2 Near expressions

A near expression is a combination of two or more regular expressions following the syntax:

     r1 ~p1 r2 ~p2 ... ~pn-1 rn

where r1, ..., rn represent regular expressions and p1, ..., pn-1 integers (written in decimal notation).

Such an expression is said to match if and only if a match of r1 is found within p1 words of a match of r2, itself found within p2 words of a match of r3, etc. The anchors used to count words are at the beginning of words (a single regexp can match several words). Example:

     nice ~2 cat

This will not only match “nice cat”, but also “nice little cat”, “nice black cat” and “cat is nice”, it will even match “nice mean cat” (!). However, it won't match “nice black and white cat”, nor “nice fat black cat”. Another example:

     nice ~4 little ~1 cat

This will of course match “nice little cat”, but also “nice black and white little cat”, “nice, little cat”, “cat little and nice” and many others. A final example:

     "knights%I" ~3 say ~2 "Ni|Nee%I" ~10 "shrubber(y|ies)"

In addition to the constraints defined by the ~3, ~2 and ~10 operators, this search expression will accomodate for some uncertainty in the writing of “Ni” versus “Nee” (or any variation in case) or “shrubbery” versus “shrubberies”.

Any whitespace (spaces, tabs or newlines) between the regexps and the ~pk operators is ignored and can therefore be used to improve the readability of a near expression.

For now, a word is defined as a contiguous sequence of characters that are either a hyphen (‘-’) or underscore (‘_’), or for which the Python unicodedata.category function returns a string that starts with “L” (letter) or “N” (number).

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2.3 Operators precedence

The ~pk operator used in near expressions has the highest priority. Then comes the ! operator, then the & and finally the |.

In other words, near expressions grab as many regexps as possible, then ! negation operators directly apply on the following expression. & and | behave as the multiplication and the addition of numbers respectively, in terms of priority.

If you don't want to ask you such questions, just use parentheses to force operators precedence!

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2.4 A complex search expression example

Here is a search expression example using all the features available (well, not all available regarding the re-module-style regexps!):

     ("bridge of death%I" | "gorge of eternal peril%I") & bridgekeeper
     & (three ~3 questions) & !hesitat

No, this is not a really useful example. And yes, the parenthesis around three ~3 questions are only here to improve readability.

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3 International

Since version 2.0, TDBSF has supported international character sets and encodings in database files. This is done through the use of Unicode in the search engine. The search expression can of course contain any Unicode character supported by Python's “re” module.

In order to use non-ASCII characters in a database file, the encoding must be specified in an encoding declaration (this is a sane practice that has been common for long among Emacs users and is now also required for Python source files, except when using the UTF-8 encoding). TDBSF refuses to work with a database file that contains non-ASCII characters and has no encoding declaration. (Actually, a UTF-8 Byte Order Mark is accepted as a substitute for an encoding declaration, but this practice is discouraged.)

The encoding declaration uses a format that is recognized by both Emacs and Python. It consists of a single line at the beginning of each database file, such as the following:

     -*- coding: utf-8 -*-

(no need to put any space before the magic delimiter -*-)

This declaration line should be followed by a blank line, then by the header of the first record of the database file. For instance:

     -*- coding: utf-8 -*-
     Header of the first record
     As many lines as necessary
     Body of the first record
     Header of the second record
     Body of the second record

Any encoding supported by Python can be used in the declaration, as long as it is ASCII-compatible (e.g., iso-8859-1, iso-8859-15, utf-8): this is necessary, because the line specifying the encoding is read before the encoding is known!

The list of valid encodings can be found at html/lib/standard-encodings.html in the documentation shipped with your Python installation (online version for Python 3 at Of course, if you use Emacs to view or edit the database files, you should make sure that the encoding name you choose is also recognized by Emacs. That is why utf-8 is preferable to utf_8. This is usually easy, because both Python and Emacs recognize a few aliases for common encodings, and Python considers spelling alternatives of encoding names that only differ in case or use a hyphen instead of an underscore as equivalent.

Different database files may use different encodings; everything is converted to Unicode in the engine before it starts searching through the contents of each file.

The command-line arguments of tdbsf-front-end are automatically decoded by Python from the user's “preferred encoding” (cf. locale.getpreferredencoding). Its output is also encoded in the same encoding (tdbsf-front-end uses the default behavior of Python 3 with respect to encoding).

The Emacs interface offers three variables to specify the encoding it uses when communicating with tdbsf-front-end: tdbsf-coding-system-for-read, tdbsf-coding-system-for-write (both defaulting to 'utf-8) and tdbsf-pythonioencoding (which defaults to "utf-8:strict"). It should not be necessary to modify these variables, as UTF-8 can encode any Unicode character.

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4 Using the search engine from a Python program

The Python tdbsf package provides a Crawler class that allows any Python program to use the TDBSF search engine. See the file for details.

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5 Future improvements

It must be easy to improve the method of specifying a set of database files, for instance by reading a set of glob-module-style patterns or allowing to explore directories recursively. The main changes would affect the interfaces. If I get any request, I'll probably improve this aspect.

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Version 2, June 1991
     Copyright © 1989, 1991 Free Software Foundation, Inc.
     51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.


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Appendix: How to Apply These Terms to Your New Programs

If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms.

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     one line to give the program's name and a brief idea of what it does.
     Copyright (C) yyyy  name of author
     This program is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
     the Free Software Foundation; either version 2 of the License, or
     (at your option) any later version.
     This program is distributed in the hope that it will be useful,
     but WITHOUT ANY WARRANTY; without even the implied warranty of
     GNU General Public License for more details.
     You should have received a copy of the GNU General Public License
     along with this program; if not, write to the Free Software
     Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.

Also add information on how to contact you by electronic and paper mail.

If the program is interactive, make it output a short notice like this when it starts in an interactive mode:

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     under certain conditions; type `show c' for details.

The hypothetical commands ‘show w’ and ‘show c’ should show the appropriate parts of the General Public License. Of course, the commands you use may be called something other than ‘show w’ and ‘show c’; they could even be mouse-clicks or menu items—whatever suits your program.

You should also get your employer (if you work as a programmer) or your school, if any, to sign a “copyright disclaimer” for the program, if necessary. Here is a sample; alter the names:

     Yoyodyne, Inc., hereby disclaims all copyright interest in the program
     `Gnomovision' (which makes passes at compilers) written by James Hacker.
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     Ty Coon, President of Vice

This General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Lesser General Public License instead of this License.

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Appendix B GNU Free Documentation License

Version 1.1, March 2000
     Copyright © 2000 Free Software Foundation, Inc.
     51 Franklin St, Fifth Floor, Boston, MA  02110-1301, USA
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     of this license document, but changing it is not allowed.

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    You may also lend copies, under the same conditions stated above, and you may publicly display copies.


    If you publish printed copies of the Document numbering more than 100, and the Document's license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.

    If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages.

    If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a publicly-accessible computer-network location containing a complete Transparent copy of the Document, free of added material, which the general network-using public has access to download anonymously at no charge using public-standard network protocols. If you use the latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public.

    It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document.


    You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:

    1. Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of previous versions (which should, if there were any, be listed in the History section of the Document). You may use the same title as a previous version if the original publisher of that version gives permission.
    2. List on the Title Page, as authors, one or more persons or entities responsible for authorship of the modifications in the Modified Version, together with at least five of the principal authors of the Document (all of its principal authors, if it has less than five).
    3. State on the Title page the name of the publisher of the Modified Version, as the publisher.
    4. Preserve all the copyright notices of the Document.
    5. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.
    6. Include, immediately after the copyright notices, a license notice giving the public permission to use the Modified Version under the terms of this License, in the form shown in the Addendum below.
    7. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document's license notice.
    8. Include an unaltered copy of this License.
    9. Preserve the section entitled “History”, and its title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section entitled “History” in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence.
    10. Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document for previous versions it was based on. These may be placed in the “History” section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission.
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    13. Delete any section entitled “Endorsements”. Such a section may not be included in the Modified Version.
    14. Do not retitle any existing section as “Endorsements” or to conflict in title with any Invariant Section.

    If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version's license notice. These titles must be distinct from any other section titles.

    You may add a section entitled “Endorsements”, provided it contains nothing but endorsements of your Modified Version by various parties—for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.

    You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.

    The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version.


    You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice.

    The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.

    In the combination, you must combine any sections entitled “History” in the various original documents, forming one section entitled “History”; likewise combine any sections entitled “Acknowledgments”, and any sections entitled “Dedications”. You must delete all sections entitled “Endorsements.”


    You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.

    You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.


    A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, does not as a whole count as a Modified Version of the Document, provided no compilation copyright is claimed for the compilation. Such a compilation is called an “aggregate”, and this License does not apply to the other self-contained works thus compiled with the Document, on account of their being thus compiled, if they are not themselves derivative works of the Document.

    If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one quarter of the entire aggregate, the Document's Cover Texts may be placed on covers that surround only the Document within the aggregate. Otherwise they must appear on covers around the whole aggregate.


    Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License provided that you also include the original English version of this License. In case of a disagreement between the translation and the original English version of this License, the original English version will prevail.


    You may not copy, modify, sublicense, or distribute the Document except as expressly provided for under this License. Any other attempt to copy, modify, sublicense or distribute the Document is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.


    The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See

    Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License “or any later version” applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation.

B.0.1 ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:

       Copyright (C)  year  your name.
       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.1
       or any later version published by the Free Software Foundation;
       with the Invariant Sections being list their titles, with the
       Front-Cover Texts being list, and with the Back-Cover Texts being list.
       A copy of the license is included in the section entitled ``GNU
       Free Documentation License''.

If you have no Invariant Sections, write “with no Invariant Sections” instead of saying which ones are invariant. If you have no Front-Cover Texts, write “no Front-Cover Texts” instead of “Front-Cover Texts being list”; likewise for Back-Cover Texts.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.

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Table of Contents


[1] No other interface is really functional as of February 2013, but the TDBSF is written so that adding interfaces is as easy as possible. :-)

[2] The fontification process tries to reflect the structure of the branch of the search expression that triggered the match by for instance giving all the elements of a matching near expression the same face (a face in Emacs is a combination of a font, a color and other such attributes).

[3] The combination of the escape character and the following one forms an escape sequence.