> ## Documentation Index > Fetch the complete documentation index at: https://docs.voiceflow.com/llms.txt > Use this file to discover all available pages before exploring further. # Overview In Voiceflow, a dialog state is assigned to a unique `userID`. This `userID` can be any string and is typically something unique that easily references the person on the session - such as an username, email, device ID, or phone number. (e.g. `user54646`, `user@gmail.com`, `1-647-424-4242`, etc.). If you're not sure what to call it just for testing purposes, you can just pick a random `userID`. The response schema consists of two main properties: 1. Stack 2. Variables We will cover each property below, as well as an overview of the Voiceflow context model. ## Stack The stack is an array of flows that are currently active in the conversation. Each flow contains: * `programID`: the ID of the flow, which can be found in the URL of the address bar `https://creator.voiceflow.com/project/{versionID}/canvas/{programID}` * `nodeID`: current block this flow is on * `variables`: flow-scoped variables * `storage`: internal flow parameters for runtime * `commands` In the example below, you can see that there are three flows available on the stack (`620e669eac2f70001cf9d85a`, `620e669eac2f70001cf9d85b` and `620e669eac2f70001cf9d85c`) and we are currently sitting on flow `620e669eac2f70001cf9d85c`, as denoted by the `nodeID` pointing to a block within this flow. Note: the `programID` of the first flow in the stack is always the `versionID` of the Agent. Example stack: ```json theme={null} { "stack": [ { "nodeID": null, "programID": "620e669eac2f70001cf9d85a", //<-- versionID of the agent "storage": {}, "commands": [], "variables": {} }, { "nodeID": null, "programID": "620e669eac2f70001cf9d85b", //<-- starting flow "storage": { "output": [ { "children": [ { "text": "What size?" } ] } ] }, "commands": [], "variables": {} }, { "nodeID": "61f40992f0e4e70a1f2328d1", "programID": "620e669eac2f70001cf9d85c",//<-- top-level flow "storage": { "outputMap": null, "output": [ { "children": [ { "text": "You can get an additional pizza for half the price today. Would you like to do that?" } ] } ] }, "commands": [], "variables": { "discount_code": "DEAL4TWO" } } ] } ``` ## Variables The two ways you can create variable keys in your Interaction Model is through: 1. Entities 2. Variables The difference between Entities and Variables is how they are assigned values at runtime. An entity value is assigned through a user interaction (e.g. utterance) whereas a variable is dynamically assigned a value from the design itself based on a user action (e.g. through an API call or custom code). Variable examples ```json theme={null} { "variables": { "type": "pepperoni", "size": "large", "amount": 6, "sessions": 0, "user_id": "1234", "timestamp": 1645112935, "platform": 0, "locale": 0, "side": 0, "intent_confidence": 100, "last_utterance": "large" } } ``` ## Voiceflow Context Model In this video, we'll explain Voiceflow's entire Context Model in more detail.