commit 450806bac6d967bdd7b85ba65d366db3ae111485
Author: Greg Back <gback@mitre.org>
Date:   Mon Dec 19 13:53:17 2016 -0500

    Add README

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+# stix2
+
+Create, parse, and interact with STIX 2 JSON content.
+
+## Installation
+
+Install with [`pip`](https://pip.pypa.io/en/stable/):
+
+```
+pip install stix2
+```
+
+## Usage
+
+
+### Creating STIX Domain Objects
+
+To create a STIX object, provide keyword arguments to the type's constructor:
+
+```python
+from stix2 import Indicator
+
+indicator = Indicator(name="File hash for malware variant",
+                      labels=['malicious-activity'],
+                      pattern='file:hashes.md5 = "d41d8cd98f00b204e9800998ecf8427e"')
+
+```
+
+Certain required attributes of all objectswill be set automatically if not
+provided as keyword arguments:
+
+- If not provided, `type` will be set automatically to the correct type. 
+  You can also provide the type explicitly, but this is not necessary:
+
+  ```python
+  indicator = Indicator(type='indicator', ...)
+  ```
+
+  Passing a value for `type` that does not match the class being constructed
+  will cause an error:
+
+  ```python
+  >>> indicator = Indicator(type='indicator', ...)
+  ValueError: Indicators must have type='indicator'
+  ```
+
+- If not provided, `id` will be generated randomly. If you provide an `id`
+  argument, it must begin with the correct prefix:
+
+  ```python
+  >>> indicator = Indicator(id="campaign--63ce9068-b5ab-47fa-a2cf-a602ea01f21a") 
+  ValueError: Indicator id values must begin with 'indicator--'
+  ```
+
+- If not provided, `created` and `modified` will be set to the (same) current
+  time.
+
+For indicators, `labels` and `pattern` are required and cannot be set
+automatically. Trying to create an indicator that is missing one of these fields
+will result in an error:
+
+```python
+>>> indicator = Indicator() 
+ValueError: Missing required field for Indicator: 'labels'
+```
+
+However, the required `valid_from` attribute on Indicators will be set to the
+current time if not provided as a keyword argument.
+
+Once created, the object acts like a frozen dictionary. Properties can be
+accessed using the standard Python dictionary syntax:
+
+```python
+>>> indicator['name']
+'File hash for malware variant'
+```
+
+TBD: Should we allow property access using the standard Python attribute syntax?
+
+```python
+>>> indicator.name
+'File hash for malware variant'
+```
+
+Attempting to modify any attributes will raise an error:
+
+```python
+>>>indicator['name'] = "This is a revised name"
+ValueError: Cannot modify properties after creation.
+```
+
+To update the properties of an object, see [Versioning](#versioning) below.
+
+Creating a Malware object follows the same pattern:
+
+```python
+from stix2 import Malware
+
+malware = Malware(name="Poison Ivy",
+                  labels=['remote-access-trojan'])
+```
+
+As with indicators, the `type`, `id`, `created`, and `modified` properties will
+be set automatically if not provided. For Malware objects, the `labels` and
+`name` properties must be provided. 
+
+### Creating Relationships
+
+STIX 2 Relationships are separate objects, not properties of the object on
+either side of the relationship. They are constructed similarly to other STIX
+objects. The `type`, `id`, `created`, and `modified` properties are added
+automatically if not provided. Callers must provide the `relationship_type`, 
+`source_ref`, and `target_ref` properties.
+
+```python
+from stix2 import Relationship
+
+relationship = Relationship(relationship_type='indicates',
+                            source_ref=indicator.id,
+                            target_ref=malware.id)
+```
+
+The `source_ref` and `target_ref` properties can be either the ID's of other 
+STIX objects, or the STIX objects themselves. For readability, Relationship
+objects can also be constructed with the `source_ref`, `relationship_type`, and
+`target_ref` as positional (non-keyword) arguments: 
+
+```python
+relationship = Relationship(indicator, 'indicates', malware)
+```
+
+### Creating Bundles
+
+STIX Bundles can be created by passing objects as arguments to the Bundle
+constructor. All required properties (`type`, `id`, and `spec_version`) will be
+set automatically if not provided, or can be provided as keyword arguments:
+
+```
+from stix2 import bundle
+
+bundle = Bundle(indicator, malware, relationship)
+```
+
+### Serializing STIX objects
+
+TBD
+
+### Versioning
+
+TBD
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