Update database diagram using MySQL Workshop

[eloquence]

Status

Ready for review

Description of Changes

Brings the database diagram up to date and includes cardinalities in crow's foot notation.

This diagram was created using MySQL Workshop, which is open source and cross-platform (while designed for MySQL, there does not appear to be a conflict between its capabilities and our relatively modest requirements). To create it, I first dumped the SQLite database and imported it using the "Import > Reverse Engineer MySQL Create Script" option. The main things I manually adjusted after that are:

• using the "indexes" section to enumerate UNIQUE constraints and foreign keys (seemed like the best fit).
• correcting the source<->star relationship to be 1:1 (side note: why this is a separate table is unclear to me)
• changing TINYINT to BOOLEAN for readability (both MySQL and SQLite store Booleans as {0,1} integers internally)

Resolves #7.

Alternatives considered

I evaluated SQLeton and ERAlchemy for fully automatic diagram generation. Neither choice offered sufficient flexibility to allow for correcting cardinalities, choosing notation styles, optimizing placement, or configuring the display of column flags such as NOT NULL or UNIQUE.

MySQL Workbench seemed a good middle ground between partial automation and partial manual effort.

SQLeton generated diagram

ERAlchemy generated diagram

Review

1. Spin up the SecureDrop Docker development environment via make dev in your SecureDrop checkout directory
2. Shell into it via docker exec -it securedrop-dev-0 bash
3. Run SQLite via sqlite3 /var/lib/securedrop/db.sqlite
4. Output the schema via .schema

Compare the output with the diagram securedrop-database.png from this PR:

1. Are the table descriptions accurate?
2. Are the relationships (including cardinalities) accurate?

Checklist (Optional)

• Doc linting (make docs-lint) passed locally
• You have previewed (make docs) docs at http://localhost:8000

[eloquence]

As a side note, this section is extremely buried in our docs right now, suggestions for reorganizing welcome for a follow-up PR :)

[eloquence]

This ensures that clicking the diagram will display the full-size version.

[sssoleileraaa]

Seems like Primary isn't showing what the primary key is, right?

[sssoleileraaa]

Oh, I see, the little yellow light bulb is the indicator. Just weird to see "PRIMARY" by itself there.

[eloquence]

I think it's supposed to be a key icon. Yeah, mysql-workbench doesn't let you name that in the "indexes" section, presumably because "there can be only one" (cue Highlander theme).

[sssoleileraaa]

correcting the source<->star relationship to be 1:1 (side note: why this is a separate table is unclear to me)

[sssoleileraaa]

^ oops i keep pressing Ctrl+Enter because SecureDrop client is training me to!!

correcting the source<->star relationship to be 1:1 (side note: why this is a separate table is unclear to me)

I don't think it normalizes anything and could be moved into the sources table

[sssoleileraaa]

lgtm!