# Depositor Defined Identifiers

Identifiers for key entities such as compounds and assays are defined within the deposition files by using Depositor Defined Identifiers (DDIs). These identifiers are created and maintained by depositors themselves. DDIs provide a way for depositors to give a meaningful unique identifier to each compound and assay in their datasets, connecting them across files for loading to the ChEMBL database.

In a basic data submission DDIs are used for compounds, assays and references, and are called [CIDX](/chembl-data-deposition-guide/deposition-overview/depositor-defined-identifiers/cidx.md), [AIDX](/chembl-data-deposition-guide/deposition-overview/depositor-defined-identifiers/aidx.md) and [RIDX](/chembl-data-deposition-guide/deposition-overview/depositor-defined-identifiers/ridx.md), respectively.  

Additional DDIs are used for internal reference between records in a dataset when more complex data is being submitted. ACT\_ID, TEOID, REGID and SAMID are used to group together supplementary data.  More information on the links between tables can be found in the [Deposition Files](/chembl-data-deposition-guide/file-structure/loader-model.md) section.

### Types of Depositor Defined ID

<table data-header-hidden><thead><tr><th width="108.33333333333331"></th><th width="310"></th><th></th></tr></thead><tbody><tr><td><strong>*IDX</strong></td><td><strong>Description</strong></td><td><strong>Primary File</strong></td></tr><tr><td><strong>AIDX</strong></td><td>Assay ID</td><td>ASSAY</td></tr><tr><td><strong>CIDX</strong></td><td>Compound ID</td><td>COMPOUND_RECORD</td></tr><tr><td><strong>RIDX</strong></td><td>Reference ID</td><td>REFERENCE</td></tr><tr><td><strong>ACT_ID</strong></td><td><strong>ACT</strong>ivity <strong>ID</strong></td><td>ACTIVITY</td></tr><tr><td><strong>TEOID</strong></td><td><strong>TE</strong>st <strong>O</strong>ccasion I<strong>D</strong></td><td>ACTIVITY</td></tr><tr><td><strong>REGID</strong></td><td><strong>RE</strong>cord <strong>G</strong>rouping <strong>ID</strong></td><td>ACTIVITY_SUPP </td></tr><tr><td><strong>SAMID</strong></td><td><strong>S</strong>upplementary <strong>A</strong>ctivity <strong>M</strong>apping <strong>ID</strong></td><td>ACTIVITY_SUPP</td></tr></tbody></table>

* DDIs are owned by the depositor; a given identifier is defined by the depositor when a deposition is first made.
* DDIs should be unique and meaningful&#x20;
  * To avoid overwriting older data
  * To make it easier to link data between files
* Depositors may use a string of up to 200 visible [UniCode](https://en.wikipedia.org/wiki/Unicode) characters to define these identifiers. &#x20;
  * We strongly encourage that DDIs are a meaningful strong of 25 to 50 characters in total and include at least 10 letters.  &#x20;
  * Meaningful strings are easier to search within a document and help the ChEMBL Team to understand your data.
* All deposited files should be [UTF-8](https://en.wikipedia.org/wiki/UTF-8) encoded.
* Subsequent use of the same identifier in future ChEMBL loads will result in the updating or overwriting of the data that was associated with this identifier when it was first loaded and is strongly discouraged.


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