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-<!doctype article PUBLIC "-//Davenport//DTD DocBook V3.0//EN" []>
-
-<!-- SGMLized by Bertrand <Bertrand.Guiheneuf@aful.org> -->
-
-<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>
-
- <!-- Definitions -->
- <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>
-
- <!-- Queries -->
- <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>
-
- <!-- Summary files -->
- <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>
-
- <!-- Incremental Indexing -->
- <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>
-
- <!-- Can I have multiple stores -->
- <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>
-
- <!-- Why all this? -->
- <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>
-
- <!-- Scenarios of usage and their solutions -->
- <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>
-
- <!-- Miscellany -->
- <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>
-
- <!-- Alternatives to the above -->
- <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>