# What is a search document?

[Search documents](https://en.wikipedia.org/wiki/Search_engine_indexing) are also modeled using [PDL](https://linkedin.github.io/rest.li/pdl_schema) explicitly.
In many ways, the model for a Document is very similar to an [Entity](entity.md) and [Relationship](relationship.md) model,
where each attribute/field contains a value that’s derived from various metadata aspects.
However, a search document is also allowed to have array type of attribute that contains only primitives or enum items.
This is because most full-text search engines supports membership testing against an array field, e.g. an array field containing all the terms used in a document.

One obvious use of the attributes is to perform search filtering, e.g. give me all the `User` whose first name or last name is similar to “Joe” and reports up to `userFoo`.
Since the document is also served as the main interface for the search API, the attributes can also be used to format the search snippet.
As a result, one may be tempted to add as many attributes as needed. This is acceptable as the underlying search engine is designed to index a large number of fields.

Below shows an example schema for the `User` search document. Note that:

1. Each search document is required to have a type-specific `urn` field, generally maps to an entity in the [graph](graph.md).
2. Similar to `Entity`, each document has an optional `removed` field for "soft deletion".
3. Similar to `Entity`, all remaining fields are made `optional` to support partial updates.
4. `management` shows an example of a string array field.
5. `ownedDataset` shows an example on how a field can be derived from metadata [aspects](aspect.md) associated with other types of entity (in this case, `Dataset`).

```
namespace com.linkedin.metadata.search

/**
 * Common fields that may apply to all documents
 */
record BaseDocument {

  /** Whether the entity has been removed or not */
  removed: optional boolean = false
}
```

```
namespace com.linkedin.metadata.search

import com.linkedin.common.CorpuserUrn
import com.linkedin.common.DatasetUrn

/**
 * Data model for user entity search
 */
record UserDocument includes BaseDocument {

  /** Urn for the user */
  urn: CorpuserUrn

  /** First name of the user */
  firstName: optional string

  /** Last name of the user */
  lastName: optional string

  /** The chain of management all the way to CEO */
  management: optional array[CorpuserUrn] = []

  /** Code for the cost center */
  costCenter: optional int

  /** The list of dataset the user owns */
  ownedDatasets: optional array[DatasetUrn] = []
}
```