# 2. Database Queries¶

## 2.1. Introduction¶

ComptoxAI is largely built around a graph database of entities, their semantic types, and the relationships that link these entities. This is implemented using Neo4j.

This document is meant to show how you can interact with these two databases to learn meaningful things about computational toxicology data. We’ll start by taking at how these data are formatted in the source database, and then we’ll discuss how to retrieve and manipulate them using ComptoxAI.

## 2.2. Graph database representation of an entity¶

For example, consider the chemical hydroxychloroquine (118-42-3 | DTXSID8023135). Hydroxychloroquine’s node in the graph database looks roughly like:

{
"identity": 32519,
"labels": [
"Chemical",
"NamedIndividual",
"Resource"
],
"properties": {
"commonName": "Hydroxychloroquine",
"inchiKey": "XXSMGPRMXLTPCZ-UHFFFAOYSA-N",
"inchi": "InChI=1S/C18H26ClN3O/c1-3-22(11-12-23)10-4-5-14(2)21-17-8-9-20-18-13-15(19)6-7-16(17)18/h6-9,13-14,23H,3-5,10-12H2,1-2H3,(H,20,21)",
"xrefDrugbank": "DB01611",
"xrefMeSHUI": "D006886",
"xrefPubchemSID": 315673741,
"xrefCasRN": "118-42-3",
"uri": "http://jdr.bio/ontologies/comptox.owl#chem_hydroxychloroquine",
"chemicalIsInCTD": true,
"chemicalIsDrug": true,
"xrefPubchemCID": 3652,
"xrefDtxsid": "DTXSID8023135"
}
}


These are mainly just identifiers, but things get more interesting when we look at relationships to other nodes in the graph database. At the time of writing, the node is directly linked to 480 other nodes in the database. Here is one of those relationships:

{
"identity": 1210864,
"start": 32519,
"end": 19842,
"type": "CHEMICALASSOCIATESWITHDISEASE",
"properties": {}
}


In this case, the start node (32519) is hydroxychloroquine, the relationship type is CHEMICAL_ASSOCIATES_WITH_DISEASE the end node (22421) is spinal cord compression:

{
"identity": 19842,
"labels": [
"Resource",
"NamedIndividual",
"Disease"
],
"properties": {
"commonName": "Spinal Cord Compression",
"uri": "http://jdr.bio/ontologies/comptox.owl#dis_spinalcordcompression",
"xrefMeSH": "D013117"
}
}


Or in other words:

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## 2.3. Finding nodes using Cypher¶

Queries in Neo4j are usually performed using the Cypher query language, which looks almost like a dialect of SQL that has been adapted to graph data. You can search for a node either directly by the node’s ID, or by any node property. In the case of hydroxychloroquine, we can find it using the following Cypher query:

$MATCH (n:Chemical {commonName: "Hydroxychloroquine"}) RETURN n;  The MATCH clause searches for entities in the database (in this case, any node with the Chemical label and the property commonName equal to "Hydroxychloroquine") and binds them to the placeholder variable n, and the RETURN clause says what to give back to the user who made the query (in this case, it just provides n without any further filtering or processing). To retrieve the same node by ID (e.g., if you ran a query previously and took note of the node’s ID), you could say: $ MATCH (n) WHERE id(n) = 32519 RETURN n;


Notice that in this case we have added a WHERE clause, which applies more complex filtering and other processing operations than can be specified in the MATCH clause alone. We also use the id() function, which (as you can probably imagine) accepts a node and returns the ID of that node as an integer value.

Of course, there are many Cypher queries that can yield the same node.

## 2.4. Finding nodes using Python¶

ComptoxAI’s Python interface makes it easier to retrieve entities from the graph database, compared to the Cypher-based methods introduced above. Let’s see how to find the same node as above, but using Python instead:

>>> from comptox_ai.db.graph_db import GraphDB
>>> db = GraphDB()
>>> db.find_node(properties={'commonName': 'Hydroxychloroquine'})


This returns the same node, just as a Python object. The value of the properties argument is a dict that can contain any node properties and associated values for those properties. Instead of properties, we can also use the node’s ID:

>>> db.find_node(node_id=32519)


## 2.5. Finding relationships using Cypher¶

Cypher’s syntax for relationships (equivalently ‘edges’) actually looks like two nodes linked by a directed edge in a graph:

\$ MATCH (n1:Chemical)-[r]->(n2:Disease) WHERE id(n1) = 32519 RETURN r;


In this case, we bind the ‘from’ node (hydroxychloroquine) to n1, the relationship to r, and the ‘to’ node (any Disease) to n2, but we only return r to the user.

## 2.6. Finding relationships using Python¶

ComptoxAI provides a method called find_relationships:

>>> from comptox_ai.db.graph_db import GraphDB
>>> db = GraphDB()
>>> db.find_relationships(from_type="Chemical", to_type="Disease", from_id=32519)


A pretty wide variety of arguments can be fed into find_relationships(), but the command will return an error if not enough arguments are provided to unambiguously resolve the search query. Please refer to GraphDB for details.