Managing Shared Definitions Safely

Why this matters

As a BI Analyst, you define metrics, dimensions, and logic that many dashboards, reports, and stakeholders depend on. A small change to a shared definition (like Revenue or Active Users) can silently break KPIs, confuse leadership, or misalign teams. Managing shared definitions safely protects trust, reduces fire drills, and keeps data work predictable.

• Real tasks: update a metric definition (e.g., exclude refunds), rename a column used by many reports, deprecate a legacy KPI, or align logic across teams.
• Risks: broken dashboards, mismatched numbers in meetings, and time lost debugging.

Concept explained simply

Shared definitions are the single sources of truth for business logic: metric formulas, calculation filters, dimension derivations, standard SQL snippets, and semantic layer or BI model files. They are assets used by many downstream users and reports.

Mental model: "Contracts and migrations"

Treat shared definitions like public APIs. Consumers rely on contracts (names, types, meanings). Changes should be versioned, reviewed, and migrated with backward compatibility whenever possible.

• Contract: the stable interface (names, semantics, data types, allowed values).
• Change: propose, review, test, release, communicate, migrate, clean up.
• Guardrails: PR reviews, tests, deprecation windows, and clear ownership.

Key principles and guardrails

• Prefer additive changes: add new fields/metrics instead of mutating existing ones.
• Use aliases or temporary shims to maintain backward compatibility during migration.
• Document the change plan: who is impacted, risk level, rollout steps, and fallback.
• Require peer review from data owners of impacted domains.
• Automate checks: unit tests for logic, schema tests for types/nulls, and linting for naming.
• Communicate timelines and deprecation dates. Avoid surprise Friday releases.
• Have an immediate revert plan for emergencies.

Worked examples

# Before (semantic.yml)
metrics:
  - name: revenue
    sql: SUM(order_amount)
    label: Revenue

# After (additive with deprecation)
metrics:
  - name: revenue
    sql: SUM(order_amount)
    label: Revenue (Deprecated; use revenue_net)
    tags: [deprecated]
  - name: revenue_net
    sql: SUM(CASE WHEN refund_flag = 0 THEN order_amount ELSE 0 END)
    label: Revenue (Net)

# Before
dimensions:
  - name: signup_date
    type: date
    sql: user.signup_ts::date

# After
dimensions:
  - name: user_signup_date
    type: date
    sql: user.signup_ts::date
  - name: signup_date
    type: date
    sql: ${user_signup_date}
    tags: [deprecated]

Workflow: Safe change lifecycle

1. Discover & scope: Define the problem, list consumers, estimate risk.
2. Design: Prefer additive changes; plan aliases, deprecation window, and tests.
3. Implement in a branch: Update definitions, add tests, and run CI locally if possible.
4. Pull Request: Include change plan, impact list, screenshots of test results, and rollback steps.
5. Review: Get approvals from data owners and an analyst who owns key dashboards.
6. Release: Merge during a safe window; monitor key metrics and error logs.
7. Communicate: Announce changes, timelines, and migration instructions.
8. Clean up: Remove deprecated aliases after the announced date.

Exercises

Complete the exercises below. Use the checklists to self-verify. Solutions are available in collapsible panels.

• Exercise 1: Plan and implement a safe metric change with deprecation.
• Exercise 2: Add ownership, tests, and approvals to protect a shared definition.

Self-check checklist

• I used additive changes or aliases first.
• I wrote a short change plan with impacts, timeline, and rollback.
• I included tests and validated results.
• I specified who must approve the change.
• I documented deprecation dates and communicated them.

Common mistakes

• Mutating an existing definition without an alias or deprecation window. Fix: add a new name first.
• Not informing dashboard owners. Fix: list impacted assets and message owners before merging.
• Releases at risky times (end of day/week). Fix: release early in the day with monitoring.
• Missing tests. Fix: add unit logic checks and schema tests for types/nullable.
• No rollback plan. Fix: define how to revert and under what signals.

Practical projects

• Create a shared semantic file for 3 core metrics (revenue_net, orders, aov). Add owners, tags, and tests.
• Refactor one legacy dimension using an alias + deprecation pattern. Write the migration note.
• Draft a team-wide “Change Plan” template with sections for risk, impact, rollout, and rollback.

Mini challenge

You discover a KPI used in the monthly exec deck has ambiguous logic. Propose a 4-step plan to clarify and migrate it without breaking the deck. Keep it concise.

Who this is for

• BI Analysts and Analytics Engineers maintaining shared metrics/dimensions.
• Analysts who own dashboards consumed by multiple teams.

Prerequisites

• Basic Git: branches, commits, pull requests.
• Comfort with SQL and reading model/semantic files (e.g., YAML).
• Familiarity with your BI tool’s model/semantic concepts.

Learning path

1. Version control basics: branching and PRs.
2. Shared definitions: contracts and consumers.
3. Tests and validation for metrics/dimensions.
4. Change planning, deprecation, and communication.
5. Release, monitor, and cleanup.

Next steps

• Adopt a lightweight change plan template for any shared-definition PR.
• Set default reviewers for high-impact files.
• Automate a minimal test suite for your top 5 KPIs.

Quick Test

Anyone can take the test for free. Only logged-in users will see saved progress and history.