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diff --git a/devel-docs/query/virtual-folder-in-depth.sgml b/devel-docs/query/virtual-folder-in-depth.sgml new file mode 100644 index 0000000000..fc85132673 --- /dev/null +++ b/devel-docs/query/virtual-folder-in-depth.sgml @@ -0,0 +1,395 @@ +<!doctype article PUBLIC "-//Davenport//DTD DocBook V3.0//EN" []> + +<!-- SGMLized by Bertrand <Bertrand.Guiheneuf@inria.fr> --> + +<article id="index"> + <artheader> + <authorgroup> + <author> + <firstname>Giao</firstname> + <surname>Nguyen</surname> + </author> + </authorgroup> + <title>An in-depth look at the virtual folder mechanism</title> + <abstract> + <para> + This document describes a different way of approaching mail + organization and how all things are possible in this brave new + world. This document does not describe physical storage issues nor + interface issues. + </para> + <para> + Historically mail has been organized into folders. These folders + usually mapped to a single storage medium. The relationship between + mail organization and storage medium was one to one. There was one + mail organization for every storage medium. This scheme had its + limitations. + </para> + <para> + Efforts at categorizations are only meaningful at the instance that + one categorized. To find any piece of data, regardless of how well + it was categorized, required some amount of searching. Therefore, any + attempts to nullify searching is doomed to fail. It's time to embrace + searching as a way of life. + </para> + <para> + These are the terms and their definitions. The example rules used are + based on the syntax for VM (http://www.wonderworks.com/vm/) by Kyle + Jones whose ideas form the basis for this. I'm only adding the + existence of summary files to aid in scaling. I currently use VM and + it's virtual-folder rules for my daily mail purposes. To date, my only + complaints are speed (it has no caches) and for the unitiated, it's + not very user-friendly. + </para> + <para> + Comments, questions, rants, etc. should be directed at Giao Nguyen + (grail@cafebabe.org) who will try to address issues in a timely + manner. + </para> + </abstract> +</artheader> + <sect1 id="definitions"> + <title>Definitions</title> + <sect2> + <title>Store</title> + <para> + A location where mail can be found. This may be a file (Berkeley + mbox), directory (MH), IMAP server, POP3 server, Exchange server, + Lotus Notes server, a stack of Post-Its by your monitor fed through + some OCR system. + </para> + </sect2> + <sect2> + <title>Message</title> + <para> + An individual mail message. + </para> + </sect2> + <sect2> + <title>Vfolder</title> + <para> + A group of messages sharing some commonality. This is the result of a + query. The vfolder maybe contained in a store, but it is not necessary + that a store holds only one vfolder. There is always an implicit + vfolder rule which matches all messages. A store contains the vfolder + which is the result of the query (any). It's short for virtual folder + or maybe view folder. I dunno. + </para> + </sect2> + <sect2> + <title>Default-vfolder</title> + <para> + The vfolder defined by (any) applied to the store. This is not the + inbox. The inbox could easily be defined by a query. A default rule + for the inbox could be (new) but it doesn't have to be. Mine happens + to be (or (unread) (new)). + </para> + </sect2> + <sect2> + <title>Folder</title> + <para> + The classical mail folder approach: one message organization per + store. + </para> + </sect2> + <sect2> + <title>Query</title> + <para> + A search for messages. The result of this is a vfolder. There are two + kinds of queries: named queries and lambda queries. More on this + later. + </para> + </sect2> + <sect2> + <title>Summary file </title> + <para> + An external file that contains pointers to messages which are matches + for a named query. In addition to pointers, the summary file should + also contain signatures of the store for sanity checks. When the term + "index" is used as a verb, it means to build a summary file for a + given name-value pair. + </para> + </sect2> + </sect1> + + <sect1> + <title>Queries</title> + <para> + Named queries are analogous to classical mail folders. Because named + queries maybe reused, summary files are kept as caches to reduce + the overall cost of viewing a vfolder. Summary files are superior to + folders in that they allow for the same messages to appear in multiple + vfolders without message duplications. Duplications of messages + defeats attempts at tagging a message with additional user information + like annotations. Named queries will define folders. + </para> + <para> + Lambda queries are similar to named queries except that they have no + name. These are created on the fly by the user to filter out or + include certain messages. + </para> + <para> + All queries can be layered on top of each other. A lambda query can be + layered on a named query and a named query can be layered on a lambda + query. The possibilities are endless. + </para> + <para> + The layerings can be done as boolean operations (and, or, not). Short + circuiting should be used. + </para> + <para> + Examples: + <programlisting> + (and (author "Giao") + (unread)) + </programlisting> + The (unread) query should only be evaluated on the results of (author + "Giao"). + <programlisting> + (or (author "Giao") + (unread)) + </programlisting> + Both of these queries should be evaluated. Any matches are added to the + resulting vfolder. + </para> + </sect1> + + <sect1> + <title>Summary files</title> + <para> + Summary files are only meaningful when applied to the context of the + default-vfolder of a store. + </para> + <para> + Summary files should be generated for queries of the form: + <programlisting> + (function "constant value") + </programlisting> + Summary files should never be generated for queries of the form: + <programlisting> + (function (function1)) + + (and (function "value") + (another-function "another value")) + </programlisting> + Given a query of the form: + <programlisting> + (and (function "value") + (another-function "another value")) + </programlisting> + The system should use one summary file for (function "value") and + another summary file for (another-function "another value"). I will + call the prior form the "plain form". + </para> + <para> + It should be noted that the signature of the store should be based on + the assumption that new data may have been added to the store since + the application generated the summary file. Signatures generated on + the entirety of the store will most likely be meaningless for things + like POP/IMAP servers. + </para> + </sect1> + + <sect1> + <title>Incremental indexing</title> + <para> + When new messages are detected, all known queries should be evaluated + on the new messages. vfolders should be notified of new messages that + are positive matches for their queries. The indexes generated by this + process should be merged into the current indexes for the vfolder. + </para> + </sect1> + + <sect1> + <title>Can I have multiple stores?</title> + <para> + I don't see why not. Again, the inbox is a vfolder so you can get a + unified inbox consisting of all new mail sent to all your stores or + your can get inboxes for each store or any combination your heart + desire. You get your cake, eat it, and someone else cleans the dishes! + </para> + </sect1> + + <sect1> + <title>Why all this?</title> + <para> + Consider the dynamic nature of the following query: + <programlisting> + (and (author "Giao") + (sent-after (today-midnight))) + </programlisting> + today-midnight would be a function that is evaluated at run-time to + calculate the appropriate object. + </para> + </sect1> + + <sect1> + <title>Scenarios of usage and their solutions</title> + <sect2> + <title>Mesage alterations</title> + <para> + This is a fuzzy area that should be left to the UI to handle. Messages + are altered. Read status are altered when a new message is read for + example. How do we handle this if our query is for unread messages? + Upon viewing the state would change. + </para> + <para> + One idea is to not evaluate the queries unless we're changing between + vfolder views. This assumes that one can only view a particular + vfolder at a time. For multi-vfolder viewing, a message change should + propagate through the vfolder system. Certain effects (as in our + example) would not be intuitive. + </para> + <para> + It would not be a clean solution to make special cases but they may be + necessary where certain defined fields are ignored when they are + changed. Some combination of the above rules can be used. I don't + think it's an easy solution. + </para> + </sect2> + <sect2> + <title>Message inclusion and exclusion</title> + <para> + Messages are included and excluded also with queries. The final query + will have the form of: + <programlisting> + (and (author "Giao") + (criteria value) + (not (criteria other-value))) + </programlisting> + Userland criterias may be a label of some sort. These may be userland + labels or Message-IDs. What are the performance issues involved in + this? With short circuiting, it's not a major problem. + </para> + <para> + The criterias and values are determined by the UI. The vfolder + mechanism isn't concerned with such issues. + </para> + <para> + Messages can be included and excluded at will. The idea is often + called "arbitrary inclusion/exclusion". This can be done by + Message-IDs or other fields. It's been noted that Message-IDs are not + unique. + </para> + <para> + I propose that any given vfolder is allocated an inclusion label and an + exclusion label. These should be randomly generated. This should be + part of the vfolder description. It should be noted that the vfolder + description has not been drafted yet. + </para> + <para> + The result is such that the rules for a given named query is: + <programlisting> + (and (user-query) + (label inclusion-label) + (not exclusion-label)) + </programlisting> + </para> + </sect2> + <sect2> + <title>Query scheduling</title> + <para> + Consider the following extremely dynamic queries: + <programlisting> + A: + (and (author "Giao") + (sent-after (today-midnight))) + + B: + (and (sent-after (today-midnight)) + (author "Giao")) + + C: + (or (author "Giao") + (sent-after (today-midnight))) + </programlisting> + Query A would be significantly faster because (author "Giao") is not + dynamic. A summary file could be generated for this query. Query B is + slow and can be optimized if there was a query compiler of some + sort. Query C demonstrates a query in which there is no good + optimization which can be applied. These come with a certain amount of + baggage. + </para> + <para> + It seems then that for boolean 'and' operations, plain forms should be + moved forward and other queries should be moved such that they are + evaluated later. I would expect that the majority of queries would be + of the plain form. + </para> + <para> + First is that the summary file is tied to the query and the store + where the query originates from. Second, a hashing function for + strings needs to be calculated for the query so that the query and the + summary file can be associated. This hashing function could be similar + to the hashing function described in Rob Pike's "The Practice of + Programming". (FIXME: Stick page number here) + </para> + </sect2> + <sect2> + <title>Archives</title> + <para> + Many people are concerned that archives won't be preserved, archives + aren't supported, and many other archive related issues. This is the + short version. + </para> + <para> + Archives are just that, archives. Archives are stores. Take your + vfolder, export it to a store. You are done. If you load up the store + again, then the default-vfolder of that store is the view of the + vfolder, except the query is different. + </para> + <para> + The point to vfolder is not to do away with classical folder + representation but to move the queries to the front where it would + make data management easier for people who don't think in terms of + files but in terms of queries because ordinary people don't think in + terms of files. + </para> + </sect2> + </sect1> + + <sect1> + <title>Miscellany</title> + <sect2> + <title>Annotations</title> + <para> + There should be a scheme to add annotations to messages. Common mail + user agents have used a tag in the message header to mark messages as + read/unread for example. Extending on this we have the ability to add + our own data to a message to add meaning to it. If we have a good + scheme for doing this, new possibilities are opened. + </para> + <sect3> + <title>Keywords</title> + <para> + When sending a message, a message could have certain keywords attached + to it. While this can be done with the subject line, the subject line + has a tendency to be munged by other mail applications. One popular + example is the "[rR]e:" prefix. Using the subject line also breaks the + "contract" with other mail user agents. Using keywords in another + field in the message header allows the sender to assist the recipient + in organizing data automatically. Note that the sender can only + provide hints as the sender is unlikely to know the organization + schemes of the recipient. + </para> + </sect3> + </sect2> + <sect2> + <title>Scope</title> + <para> + Let us assume that we have multiple stores. Does a query work on a + given store? Or does it work on all stores? Or is it configurable such + that a query can work on a user-selected list of stores? + </para> + </sect2> + </sect1> + + <sect1> + <title>Alternatives to the above</title> + <para> + Jim Meyer (purp@selequa.com) is putting some notes on where + annotations needs to be located. They'll be located here as well as + any contributions I may have to them. + </para> + </sect1> +</article> |