## Python SDK key concepts

URL: https://docs.atlan.com/product/capabilities/build-apps/sdks/python/concepts

> Core Python SDK concepts: typedefs define each asset type's data model in Atlan, all types extend the Asset base class, and this hierarchy underpins search, enrichment, and custom metadata.

# Other important concepts

## Type definitions

Type definitions (or **typedefs** for short) describe the properties and relationships that each different *type* of asset can have in Atlan.

> **Tip: Type definitions are the *structure* for metadata**
>
> In an object-oriented programming sense, think of a type definition as the ***class*** itself. They describe the underlying *data model* of Atlan.

For example:

- The model for database tables in Atlan is defined by the `Table` typedef.
- The `Table` typedef describes characteristics unique to database tables, such as column counts and row counts.
- The `Table` typedef inherits from an `Asset` typedef. (As do most other objects in Atlan.)
- The `Asset` typedef describes characteristics that apply to all of these objects, such as certificates and announcements.

```mermaid
classDiagram
 class Asset {
 <<abstract>>
 name
 qualifiedName
 certificateStatus
 certificateStatusMessage
 announcementType
 announcementTitle
 announcementMessage
 ...
 assignedTerms()
 }
 class Table {
 columnCount
 rowCount
 atlanSchema()
 columns()
 }
 class Column {
 dataType
 isNullable
 table()
 }
 Asset <|-- Table : extends
 Asset <|-- Column : extends
```

## Special assets

While all assets follow the above principles, there are two types of assets to be aware of that have further specific uses in Atlan.

### Connections

```mermaid
classDiagram
 class Connection {
 ...
 connector[Name|Type]
 ...
 }
```

**Connections** play several important roles:

- They form the basis of Atlan's access control policies.
- Their `connectorName` property (renamed `connectorType` in some SDKs) decides the [icon](https://docs.atlan.com/llms/platform/types/llms.txt) Atlan will use for assets contained within the connection.

### Processes

**Processes** form the basis for Atlan's data lineage. They define how data inputs (*sources*) are translated into data outputs (*targets*).

Without a process asset to link these upstream and downstream assets, you can't have data lineage in Atlan.

```mermaid
graph LR
 s1[(Source 1)]
 s2[(Source 2)]
 s3[(Source 3)]
 t1[(Target 1)]
 t2[(Target 2)]
 p([Process])
 s1 & s2 & s3-->|upstream|p-->|downstream|t1 & t2
```

---

## Tags

[Tags](https://ask.atlan.com/hc/en-us/articles/6751823790609) give you a way to classify and group assets in different ways, for example:

- By industry standard information security or sensitivity schemes (for example: PII)
- By department or business domain (for example: HR, Finance, Marketing, and so on)
- By key characteristic for alerting (for example: data quality issue, load failure, or similar)
- Really any other way you want to group together your assets

### Propagation

What's special about tags?

Atlan can [*propagate*](https://ask.atlan.com/hc/en-us/articles/7781076790289) tags for you automatically, to related assets:

- From upstream assets to downstream assets (via lineage)
- From parent assets to child assets (for example, from a table to all of its columns)
- From a term to all of its linked assets

 This becomes particularly powerful when using tags to represent key information you want to let your users know about. For example:

#### Tagging problematic assets

- If you find a problem on an asset, you can tag that asset as having a known issue.
- With propagation, Atlan will *automatically* tag all downstream (impacted) assets as having a known issue as well.
- Even better, you can see from that propagated tag which upstream assets are the source of that known issue.

#### Tagging sensitive assets

- You can create a glossary of terms core to your business like customer details, accounts, etc.
- You can assign the terms in that glossary to the data assets that hold that information.
- You can then tag the terms with sensitivity ratings (like PII, Confidential, Public, etc).
- With propagation, Atlan will *automatically* tag all related data assets with those same sensitivity ratings.
- Even better, any assets or fields *derived* from those assets (even if named differently) will be propagated that sensitivity rating as well.

### Branding

You can also "brand" tags to provide quick visual distinction:

- Choose from a predefined list of icons
- Apply a color to the tag
- Or even upload your own image to use as an icon to represent the tag

### Access control

Tags can also be used to control access to assets, through [purposes](https://ask.atlan.com/hc/en-us/articles/4418690792849). When combined with propagation, you gain a very powerful, automated means to protect your most sensitive data.

---

## Custom metadata

[Custom metadata](https://ask.atlan.com/hc/en-us/articles/6755053022225) gives you a way to extend the built-in [types](#type-definitions) with your own attributes.

Structurally custom metadata is composed of:

- An overall name (sometimes referred to as a "set")
- Individual attributes contained within that "set"
- (Optional) Restrictions on which assets can possess values for the custom metadata

> **Warning: Runtime resolution**
>
> Note that unlike built-in types and attributes, custom metadata can only be resolved at runtime. Therefore custom metadata attributes aren't strongly-typed in the SDKs the way built-in types and attributes are—they must be handled a little differently.

### Badges

What's special about custom metadata?

1. Firstly, custom metadata gives you a way to define your own attributes for assets.
2. In addition, on top of custom metadata attributes you can create [badges](https://ask.atlan.com/hc/en-us/articles/8603249978781) to callout important information on assets.

 ### Branding

You can also "brand" custom metadata to provide quick visual distinction:

- Choose from a predefined list of emojis
- Or even upload your own image to use as an icon to represent the custom metadata

This "branding" will also be used for any badges you create over the custom metadata attributes.

_Last updated: 19 May 2026._

---

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