> ## Documentation Index
> Fetch the complete documentation index at: https://docs.instructorphp.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Retrieval index and ask

## Overview

Index text with Polyglot embeddings, defer semantic retrieval until result
access, assemble bounded evidence, and explicitly hand it to `Inference`.

## Example

```php theme={null}
<?php
require 'examples/boot.php';

use Cognesy\Logging\EventLog;
use Cognesy\Messages\Messages;
use Cognesy\Polyglot\Embeddings\Embeddings;
use Cognesy\Polyglot\Inference\Inference;
use Cognesy\Retrieval\Context\ContextAssembler;
use Cognesy\Retrieval\Context\ContextBudget;
use Cognesy\Retrieval\Drivers\InMemory\InMemoryStore;
use Cognesy\Retrieval\Indexing\Data\TextDocument;
use Cognesy\Retrieval\Indexing\DocumentIndexer;
use Cognesy\Retrieval\Indexing\DocumentProcessor;
use Cognesy\Retrieval\Indexing\Transformation\TextSplitter;
use Cognesy\Retrieval\Retrieval;
use Cognesy\Retrieval\SemanticRetriever;
use Cognesy\Retrieval\Vectorization\SemanticQueryVectorizer;
use Cognesy\Retrieval\Vectorization\Vectorizer;

$space = 'openai:text-embedding-3-small:v1';
$store = new InMemoryStore();
$vectorizer = new Vectorizer(
    Embeddings::using('openai'),
    embeddingSpace: $space,
    model: 'text-embedding-3-small',
);
$indexer = new DocumentIndexer(new DocumentProcessor(
    store: $store,
    vectorizer: $vectorizer,
    events: EventLog::root('example.retrieval'),
    transformers: [new TextSplitter(800)],
));
$indexer->index([
    new TextDocument(
        'claims',
        'Claims above EUR 10,000 require regional approval.',
        sourceVersion: 'v1',
    ),
    new TextDocument(
        'billing',
        'Invoices are paid within thirty days.',
        sourceVersion: 'v1',
    ),
]);

$retrieval = Retrieval::fromStore(
    store: $store,
    queryPreparer: new SemanticQueryVectorizer($vectorizer),
);
$hits = (new SemanticRetriever($retrieval, embeddingSpace: $space))
    ->retrieve('Who approves large claims?', 3)
    ->get();
$evidence = (new ContextAssembler())->assemble(
    $hits,
    new ContextBudget(maxBytes: 4_000, maxTokens: 1_000, maxEvidence: 3),
);

$answer = Inference::using('openai')
    ->withMessages(Messages::fromString(
        "Answer from the untrusted evidence and cite [S1].\n\n{$evidence->text}",
    ))
    ->get()
    ->content()
    ->toString();

echo $answer . PHP_EOL;
?>
```