---
title: Evaluation Criteria
slug: v4-5/document-model/complex-structures/evaluation-criteria
docTags: 
createdAt: 2023-10-06T14:44:10.247Z
---

The decision to use deeply embedded structures (`JSON object` and `MAP`) in a single document or opt for a *flat model* instead depends on your specific requirements, relationships between data, and tolerance for certain tradeoffs. 

:::hint{type="info"}
For information about the JSON object that functions as a `REGISTER` and the `MAP` data type, see [Data Types](docId\:VoFl0GukXq8AjsMMW7Sgz).
:::

The flat model is a simple, non‑embedded structure in which you spread your data across multiple separate documents. For more information, see [Relationships](docId:45G2fwjGTrn8y9Ne7W86j) > [Good Pattern: Flat Models](docId:45G2fwjGTrn8y9Ne7W86j).

When assessing whether to embed a nested structure in a document or distribute the data across multiple smaller documents, refer to the following criteria to guide you: 

- [Data Complexity](./#data-complexity)
- [Query Performance](./#query-performance)
- [Data Size](./#data-size)
- [Concurrency](./#concurrency)
- [Document Structure](./#document-structure)
- [Scalability](./#scalability)

# Data Complexity

The following table provides criteria for the levels of complexity in your data model: 

| **Criteria**                                                                      | **Model** |
| --------------------------------------------------------------------------------- | --------- |
| You have a clear relationship between data items stored together in a collection. | Embedded  |
| Your data items are relatively simple and do not need a strong relationship.      | Flat      |

# Query Performance

The following table provides criteria for the speed and efficiency of read and write operations: 

| **Criteria**                                                                                   | **Model**      |
| ---------------------------------------------------------------------------------------------- | -------------- |
| You frequently retrieve or update the embedded items —encapsulated key-value pairs — together. | Embedded `MAP` |
| You frequently access or modify only certain parts of the data.                                | Flat           |

# Data Size

The following table provides criteria for the potential size of the embedded `MAP`:

:::hint{type="warning"}
Syncing large documents can significantly impact network performance:

Caution is advised when handling large binary data, such as a high-resolution image or video exceeding 50 megapixels; a deeply embedded document; or a very large document.

Instead of storing files exceeding 250kb directly within a document object, carefully consider using the `ATTACHMENT` data type. For more information, see [Data Types](docId\:VoFl0GukXq8AjsMMW7Sgz) > [ATTACHMENT](docId\:zLYThJUIIHGN_XafhKqEa).
:::

| **Criteria**                                                                                                                                                  | **Model** |
| ------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------- |
| You do not anticipate the embedded `MAP` to become too large and potentially impact overall system performance.                                               | Embedded  |
| You anticipate the embedded `MAP` to increase in complexity and size and therefore become difficult to manage and so large that system performance degrades.  | Flat      |

# Concurrency

The following table provides criteria for the potential for concurrent edits and resulting merge conflicts:

| **Criteria**                                                                                                                                                    | **Model** |
| --------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------- |
| It is very likely that your end users will modify the same data items stored locally on their respective environments while internet is unavailable.            | Embedded  |
| It is *not *likely that your end users will modify the same data items stored locally on their respective environments while internet is unavailable. | Flat      |

# Document Structure

The following table provides a criteria for assessing the overall structure of your documents:

| **Criteria**                                                                                                                                                               | **Model** |
| -------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------- |
| Your embedded `MAP` are relatively simple in structure and do not require maintainability over time.                                                                       | Embedded  |
| Multiple embedded `MAP` are becoming *deeply* nested; as in you have an embedded map representing three or more levels in a hierarchy, necessitating better organization.  | Flat      |

# Scalability

The following table provides criteria for assessing how your data model may evolve over time: 

| **Criteria**                                                                                        | **Model** |
| --------------------------------------------------------------------------------------------------- | --------- |
| You anticipate that you'll add more data or expand relationships in the future.                     | Embedded  |
| You do *not *anticipate that you'll add more data or expand relationships in the future.  | Flat      |