Overview

Syncslides uses Syncbase for data storage and communication between users' devices.

Detailed Design

// Deck is the metadata for a set of slides.
struct Deck {
  Title string
  Thumbnail []byte
}

// Slide contains the image content for the slide.
struct Slide {
  // A low-res version of the image stored as PNG.
  Thumbnail []byte
  // A high-res version of the image stored as PNG.
  Fullsize Blobref
}

// Note contains private-to-the-user notes for a specific slide.
struct Note {
  Text string
}

// Presentation represents a live display of a Deck.
struct Presentation {
  // If the presenter has handed control of the presentation to an audience member,
  // driver will be present.  When the presenter takes back control, this
  // will switch back to the empty string.
  Driver ?Person  // ? means optional.
}

// Person represents either an audience member or the presenter.
struct Person {
  FirstName string
  LastName string
}

// CurrentSlide contains state for the live presentation.  It is separate from the
// Presentation so that the presenter can temporarily delegate control of the
// CurrentSlide without giving up control of the entire presentation.
struct CurrentSlide {
  // The number of the slide that the presenter is talking about.
  Num int32
  // In the future, we could add markup/doodles here.  That markup would be transient
  // if stored here.  Maybe better to put it in a separate row...
}

// Question represents a member of the audience asking a question of the presenter.
// TODO(kash): Add support for the user to type in their question.  Right now, they
// need to ask their question verbally.
struct Question {
  // The person who asked the question.
  Questioner Person
  // Time when the question was asked in milliseconds since the epoch.
  Time int64
  // Track whether this question has been answered.
  Answered bool
}

Table Decks

A Deck is a set of slides plus metadata. It can be used in multiple presentations. It is owned by the presenter, and the audience has read-only access.

The deck is immutable because we use the simple scheme of ordering slides by their key (see example below). The other tables refer to the slides by these hardcoded names, so those references would break if we allowed deck mutations.

<deckId>            --> Deck
<deckId>/slides/1   --> Slide
<deckId>/slides/2   --> Slide
<deckId>/slides/3   --> Slide
...

Table Notes

Notes are private to a user. They are sparse in that if a user does not have any notes for a slide, the corresponding row is not present.

The lastViewed row contains the timestamp that the user last viewed the presentation in milliseconds since the epoch. TODO(kash): Can we replace this with vdl.Time? Does it work in Java?

<deckId>/LastViewed  --> int64
<deckId>/slides/1    --> Note
<deckId>/slides/5    --> Note

Table Presentations

A presentation represents the live state of a presenter displaying a deck to an audience.

<deckId>/<presentationId>                         --> Presentation
<deckId>/<presentationId>/CurrentSlide            --> CurrentSlide
<deckId>/<presentationId>/questions/<questionId>  --> Question

Syncgroups

There are multiple syncgroups as part of a live presentation.

• The presentation syncgroup contains:
  • Table: Decks, Prefix: <deckId>
    • ACL: Presenter: RWA, Audience: R
  • Table: Presentation, Prefix: <deckId>/<presentationId>
    • ACL: Presenter: RWA, Audience: R
• The notes syncgroup contains:
  • Table: Notes, Prefix: <deckId>
    • ACL: Person who wrote the notes: RWA

Delegation

We want to be able to temporarily delegate control of the presentation to an audience member. The presenter will do this by writing the audience member's name to the Presentation struct in the Presentations table. The presenter will also set the ACL on the CurrentSlide so that audience member can write it. When the presenter wants control again, she will reverse these steps.

Questions

When a user wants to ask a question, their device needs to write a Question struct into the Presentations table. The <deckId>/<presentationId>/questions prefix will be writable to everyone. When the questioner adds a question, they will also add an ACL just for that row. The ACL will give write access to that user and to the presenter.