WimpyPoint II

Overview

• Integration with ACS (e.g., fixing naming conventions and using ACS users).
• Allowing authors to freeze presentations, and later view older versions of the presentation or revert to a previous, frozen version.
• Unlimited length for slide content.
• Allowing files and images to be attached to slides.
• User/group-based access control (ACL lists).
• Implementing data mirroring (copying everything to a backup server nightly).
• Allowing users to upload and maintain their own style sheets.
• Allowing viewers to override authors' style information.
• User-interface improvements in authoring mode.

Data Model

Naming Conventions

ACS Integration

Access Control

• read access, allowing the user to view the presentation even if it is not public.
• write access, allowing the user (a "collaborator") to edit the presentation.
• admin access, allowing the user (an "owner") to change the ACL, invite collaborators, freeze the presentation, delete the presentation, etc.

An administrator can invite another user to collaborate (or co-own the presentation) by adding him to the ACL list. (WimpyPoint will notify the invitee via E-mail if requested.) If the user is not already an ACS user (and thus cannot be added to the ACL), WimpyPoint will issue a "ticket" (a row in the wp_user_access_ticket) which can be redeemed for an ACL entry once the account is created. The ticket is protected by a secret text string which is encoded into the URL sent to the invitee as part of the invitation request.

Versioning

• To obtain the most recent version of a slide ss, use a query like

  SELECT *
  FROM   wp_slides sl
  WHERE  slide_id = ss
  AND    checkpoint = (SELECT MAX(checkpoint) FROM wp_slides WHERE slide_id = sl.slide_id)
  AND    deleted_in_checkpoint IS NULL
  

  In other words, we select the row with the maximum checkpoint.
• To obtain the slide as it was when we set checkpoint nn:

  SELECT *
  FROM   wp_slides
  WHERE  slide_id = ss
  AND    checkpoint = (SELECT MAX(checkpoint) FROM wp_slides
                       WHERE  slide_id = sl.slide_id
                       AND    checkpoint <= nn)
  AND    (deleted_in_checkpoint IS NULL OR deleted_in_checkpoint > nn)
  

  Again, we select the row with the maximum checkpoint, this time subject to the constraint that the checkpoint is nn or earlier (i.e., get the latest change before nn).

  Note that these previous two queries are not specific to querying for single slides; for instance, to view the most resent version of an entire presentation pp, simply change slide_id = ss to presentation_id = pp and add ORDER BY sort_key.

• To modify a slide, we check and see if the current version of the slide has checkpoint set to the most recent checkpoint for the presentation (stored in wp_presentations.checkpoint). If so, we modify the slide in-place using an UPDATE; if not, a checkpoint has been set since the last modification so we must create a new row in the wp_slides table referring to the most recent checkpoint.
• To add a slide, we simply add a row to wp_slides with checkpoint set to the most recent checkpoint for the presentation.
• To delete a slide (assuming that the current checkpoint for the presentation is cc):

  DELETE FROM wp_slides
  WHERE  slide_id = ss AND checkpoint = cc
  
  UPDATE wp_slides
  SET    deleted_after_checkpoint = cc
  WHERE  presentation_id = pp
  

Images and Attachments

Users can upload attachments and images to be displayed inline (embedded in the page) or separately. These are stored in a separate table (wp_attachments) so that multiple versions of a presentation can share them.

Styles

Individual readers can override authors' style preferences, e.g., if the reader prefers black text on white text because he/she needs to deal with a finicky projector.

Implementation

• Migrate the existing code to the new data model (this includes ACS integration).
• Clean up the authoring interface.
• Add support for versioning.
• Implement unlimited slide length and image/attachment upload.
• Add access control.
• Set up data mirroring (the backup server will run WimpyPoint, but with editing features disabled).
• Implement the new style management system.

Migration

• Creates an ACS user entry for each WimpyPoint user.
• For each presentation in the old WimpyPoint, reads the presentation and slides and inserts the appropriate rows into tables in the new data model, mapping WimpyPoint users to ACS users, ownership privileges to ACL entries, etc.