[Search documents](https://en.wikipedia.org/wiki/Search_engine_indexing) are also modeled using [PDSC](https://linkedin.github.io/rest.li/DATA-Data-Schema-and-Templates) 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".
This is captured in [BaseDocument](../../metadata-models/src/main/pegasus/com/linkedin/metadata/search/BaseDocument.pdsc), which is expected to be included by all documents.
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`).
```json
{
"type": "record",
"name": "BaseDocument",
"namespace": "com.linkedin.metadata.search",
"doc": "Common fields that apply to all documents",
"fields": [
{
"name": "removed",
"type": "boolean",
"doc": "Whether the entity has been removed or not",
"optional": true,
"default": false
}
]
}
```
```json
{
"type": "record",
"name": "UserDocument",
"namespace": "com.linkedin.metadata.search",
"doc": "Data model for user entity search",
"include": [
"BaseDocument"
],
"fields": [
{
"name": "urn",
"type": "com.linkedin.common.CorpuserUrn",
"doc": "Urn for the user"
},
{
"name": "firstName",
"type": "string",
"doc": "First name of the user",
"optional": true
},
{
"name": "lastName",
"type": "string",
"doc": "Last name of the user",
"optional": true
},
{
"name": "management",
"type": {
"type": "array",
"items": "com.linkedin.common.CorpuserUrn"
},
"doc": "The chain of management all the way to CEO",
