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Vectors & similarity search

Trace a worked example

From goal to measurement to ship-or-abort for vectors and similarity on the internal FAQ semantic search.

~12 min this pageWorked example

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Goal: improve the internal FAQ semantic search using vectors and similarity without breaking protected slices.

Mechanism reminder for vectors and similarity: Embed text to d numbers, optionally normalize, score with cosine/dot/Euclidean, take top-k or threshold.

Baseline and shock: cos(a,b)=(a·b)/(||a|| ||b||)=(1×2+2×4)/(√5×√20)=10/10=1

Tradeoff in play for vectors and similarity: More dimensions can represent richer patterns but cost memory and search time. Cosine removes magnitude information, which may help or discard signal. A top-k query always returns something, while a threshold can abstain but must be calibrated. Generic embeddings may underperform in specialized domains.

Ship decision: Cosine on normalized 768-d with k=8 plus keyword OR for policy codes; rebuild on model change.

Rollback triggers for vectors and similarity must cite recall@k, precision@k, abstain quality, ID-slice recall. If you cannot name a tolerated regression on the internal FAQ semantic search, do not promote the change.

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Make it operational

Keep the vectors and similarity decision record beside the internal FAQ semantic search code paths that implement it. Future you will not remember why a default exists unless the evidence is linked from the config for vectors and similarity.

Also pin one numeric memory from this vectors and similarity chapter: cos(a,b)=(a·b)/(||a|| ||b||)=(1×2+2×4)/(√5×√20)=10/10=1 That number is not decoration; it is a template for how claims about vectors and similarity on the internal FAQ semantic search should look in design docs. Scoped specifically to vectors and similarity / internal FAQ semantic search / worked-trace.

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Common mix-ups

People confuse vectors and similarity with neighboring buzzwords when debugging the internal FAQ semantic search. Before changing prompts, ask whether the broken stage was evidence gathering, the vectors and similarity judgment itself, validation, or the product action. Fixing the wrong stage creates folklore (“we tried vectors and similarity and it failed”) that blocks the next team on the internal FAQ semantic search. Scoped specifically to vectors and similarity / internal FAQ semantic search / worked-trace.

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Rehearsal (vectors-and-similarity/worked-trace)

Write a five-line artifact for this page: goal, inputs, check, owner, stop rule. Invent one fluent failure that the check would catch. Keep details specific to vectors and similarity rather than generic AI advice.

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Rehearsal (vectors-and-similarity/worked-trace)

Write a five-line artifact for this page: goal, inputs, check, owner, stop rule. Invent one fluent failure that the check would catch. Keep details specific to vectors and similarity rather than generic AI advice.

Read

Rehearsal (vectors-and-similarity/worked-trace)

Write a five-line artifact for this page: goal, inputs, check, owner, stop rule. Invent one fluent failure that the check would catch. Keep details specific to vectors and similarity rather than generic AI advice.

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Chapter close 1

For vectors and similarity, add acceptance test 1: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 2

For vectors and similarity, add acceptance test 2: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 3

For vectors and similarity, add acceptance test 3: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 4

For vectors and similarity, add acceptance test 4: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 5

For vectors and similarity, add acceptance test 5: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 6

For vectors and similarity, add acceptance test 6: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 7

For vectors and similarity, add acceptance test 7: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 8

For vectors and similarity, add acceptance test 8: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 9

For vectors and similarity, add acceptance test 9: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 10

For vectors and similarity, add acceptance test 10: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 11

For vectors and similarity, add acceptance test 11: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 12

For vectors and similarity, add acceptance test 12: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 13

For vectors and similarity, add acceptance test 13: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 14

For vectors and similarity, add acceptance test 14: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 15

For vectors and similarity, add acceptance test 15: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 16

For vectors and similarity, add acceptance test 16: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 17

For vectors and similarity, add acceptance test 17: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 18

For vectors and similarity, add acceptance test 18: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 19

For vectors and similarity, add acceptance test 19: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 20

For vectors and similarity, add acceptance test 20: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 21

For vectors and similarity, add acceptance test 21: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 22

For vectors and similarity, add acceptance test 22: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 23

For vectors and similarity, add acceptance test 23: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 24

For vectors and similarity, add acceptance test 24: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 25

For vectors and similarity, add acceptance test 25: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 26

For vectors and similarity, add acceptance test 26: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 27

For vectors and similarity, add acceptance test 27: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 28

For vectors and similarity, add acceptance test 28: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 29

For vectors and similarity, add acceptance test 29: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 30

For vectors and similarity, add acceptance test 30: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 31

For vectors and similarity, add acceptance test 31: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 32

For vectors and similarity, add acceptance test 32: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 33

For vectors and similarity, add acceptance test 33: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 34

For vectors and similarity, add acceptance test 34: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 35

For vectors and similarity, add acceptance test 35: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

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Chapter close 36

For vectors and similarity, add acceptance test 36: evidence source, threshold, and signer. Keep it unique to this chapter's scenario.

Go deeper

Before you start

Why this matters

List the constraints (latency, cost, privacy, review capacity) that any vectors and similarity change must respect for the internal FAQ semantic search.

In the wild

See how this idea shows up as a product and a company — then come back to the lesson. Skills transfer across vendors.

Check your understanding

Page assessment

Answer from memory. Completion is saved from this evidence, not from opening the next page.

1. What is one idea from this page you would apply, and what evidence would you check?

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