# Defining Models

## Models

The below Kye script defines a `User` table. Table names must be uppercased.

```
User(id)(username) {
  id: Number
  username: String
  name: String
  age?: Number

  assert age > 0 & age <= 120
}
```

## **Indexes**

The name of the table is followed by its index definition. The `(id)(username)` means that we expect both the `id` or `username` columns to be able to uniquely identify a record.

Composite indexes are defined by listing multiple column names within a single set of parenthesis ex. `(id, username)`

## **Columns**

Column names must start with a lowercase and not contain spaces or other special characters. If the source data has column names that don't follow these rules, then you can specify the full column name in quotes after the column name.

```
  id "User Id": Number
```

The column definitions specify the value type as `Number`, `String` or `Boolean`. More data types like date/time and user defined types are coming soon.

You can specify whether the column allows null values by prefixing the colon with a `?`

```
age?: Number
```

You can also specify if the column allows multiple values (like an array of values) by using `+` if you expect at least one value, or `*` if it is okay to have no values.

```
# Expect at least one version
versions+: String

# It's okay for a post to have no tags
tags*: String 
```

## **Assertions**

You can specify extra assertions through the `assert` keyword. Just write an expression that evaluates to true or false, and the rows that evaluate to false will be flagged. You can reference columns by their names.


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