Update field mapping documentation for Security Analytics

_security-analytics/sec-analytics-config/detectors-config.md

@@ -9,9 +9,9 @@ nav_order: 15
 
 Security Analytics provides the options and functionality to monitor and respond to a wide range of security threats. Detectors are the essential components that determine what to look for and how to respond to those threats. This section covers their creation and configuration. 
 
-## Step 1. Defining a detector
+## Step 1. Define the detector
 
-Defining a new detector involves naming the detector, selecting a data source and detector type, and specifying a detector schedule. After defining a detector, you can also configure field mappings and set up alerts. Follow the steps in this section to accomplish all three of these setup tasks.
+Defining a new detector involves naming the detector, selecting a data source and detector type, and specifying a detector schedule. You can also create alerts for the detector at this stage, although there are options to create alerts in other areas of the interface. Follow the steps in this section to define a new detector.
 
 1. On the Detectors page, select the **Create detector** button. The Define detector page opens.
 1. Give the detector a name and, as an option, add a description for the detector. 
@@ -28,42 +28,65 @@ Defining a new detector involves naming the detector, selecting a data source an
 * Use the **Log type**, **Rule severity**, and **Source** dropdown menus to filter the rules you want to select from. 
 * Use the **Search** bar to search for specific rules.
 
-    To quickly select one or more known rules and dismiss others, first deselect all rules by moving the **rule name** toggle to the left, then search for your target rule names and select each individually by moving its toggle to the right.
+    To quickly select one or more known rules and dismiss others, first deselect all rules by moving the **Rule name** toggle to the left, then search for your target rule names and select each individually by moving its toggle to the right.
     {: .tip }
 
 1. In the **Detector schedule** section, set how often the detector will run. Specify a unit of time and a corresponding number to set the interval.
 1. Select the **Next** button in the lower-right corner of the screen to continue. The Configure field mapping page appears.
 
-## Step 2. Making field mappings
+## Step 2. Create field mappings
 
-Field mapping matches field names for the rule with field names from the log being used to provide data. The mappings are automatically applied once the detector is defined in previous steps. This page offers the user the option to map log-specific field names to the internal rule field names.
+The field mapping step matches field names from the rule with field names from the log index being used to provide data. Creating field mappings allows the system to accurately pass event data from the log to the detector and then use the data to trigger alerts.
 
-For example, if you prefer to have the log field name UserID rather than EventID correspond to the event_uid rule field name, you can use the **Log field name** dropdown menu to select **UserID**.
+The data source (log index), log type, and detection rules specified in the first step determine which fields are available for mapping. For example, when "Windows logs" is selected as the log type, this parameter, along with the specific detection rules, determines the list of rule field names available for the mapping. Similarly, the selected data source (log index) determines the list of log field names that are available for the mapping.
 
-<img src="{{site.url}}{{site.baseurl}}/images/Security/field_map.png" alt="Rule and log field mapping example">
+#### A note on field names
 
-To make any changes to the automatically populated mappings, use the dropdown arrows across from the rule field names to specify a preferred log field name for the mapping. After completing the mappings, select the **Next** button in the lower-right corner of the screen. The Set up alerts page appears and displays settings for an alert trigger.
+The field mapping process requires that you are familiar with the field names in the log index and have an understanding of the data contained in those fields. If you have an understanding of the log fields in the index, the mapping is typically a simple and straightforward process.
 
-## Step 3. Setting up alerts
+Security Analytics takes advantage of prepackaged Sigma rules for security event detection. Therefore, the rule field names are derived from a Sigma rule field standard. To make them easier to identify, however, we create aliases for the Sigma rule fields based on the open source Elastic Common Schema (ECS) specification. These alias rule field names are the field names used in these steps. 
 
-The third step in creating a detector involves setting up alerts. Alerts are configured to create triggers that, when matched with a set of detection rule criteria, send a notification of a possible security event. You can select the criteria (rules, rule severity, and tags) in any combination to define a trigger. Once a trigger is defined, the alert setup lets you choose the channel on which to be notified and provides options for customizing a message for the notification.
+Although the ECS rule field names are largely self explanatory, you can find pre-defined mappings of the Sigma rule field names with ECS rule field names, for all supported log types, in the GitHub Security Analytics repository. First navigate to the [OSMappings](https://github.com/opensearch-project/security-analytics/tree/main/src/main/resources/OSMapping) folder, select the folder named for the log type, and open the `fieldmappings.yml` file. For example, to see the Sigma rule fields that correspond to ECS rule fields for the Windows log type, open the [fieldmappings.yml file](https://github.com/opensearch-project/security-analytics/blob/main/src/main/resources/OSMapping/windows/fieldmappings.yml) in the **windows** folder.
 
-At least one alert condition is required before a detector can begin generating findings.
-{: .note }
+### Pending field mappings
 
-You can also configure alerts from the Findings window. To see how to set up alerts from the Findings window, see [The findings list]({{site.url}}{{site.baseurl}}/security-analytics/usage/findings/#the-findings-list). A final option for adding additional alerts is to edit a detector and navigate to the **Alert triggers** tab, where you can edit existing alerts as well as add new ones. For details, see [Editing a detector]({{site.url}}{{site.baseurl}}security-analytics/usage/detectors/#editing-a-detector).
+Once you navigate to the **Configure field mapping** page, the system attempts to automatically map fields between the two sources. Those field names that are not automatically mapped appear in the **Pending field mapping** table. In this table you can manually map rule fields to log fields, as shown in the following image.
+<br><img src="{{site.url}}{{site.baseurl}}/images/Security/pending-mappings.png" alt="Field mapping example for pending mappings" width="85%">
 
-To set up an alert for a detector, continue with the following steps:
+* The Rule field name column lists field names based on all of the pre-packaged rules associated with the selected log type.
+* The log field name column includes a dropdown list for each of the rule fields. Each dropdown list contains field names extracted from the log index.
+* To map a rule field name to a log field name, use the dropdown arrow to open the list of log fields and select the log field name from the list. To search for names in the log field list, enter text in the **Select a mapping field** box.
+<br><img src="{{site.url}}{{site.baseurl}}/images/Security/log-field.png" alt="Field mapping example for pending mappings" width="60%">
+* Once the log field name is selected and mapped to the rule field name, the icon in the Status column to the right changes to a green check mark.
+* Make as many matches between field names as possible to complete an accurate mapping for rule and log fields. 
+
+### Default field mappings
+
+The **Default mapped fields** table contains mappings that the system made automatically after defining the detector. As shown in the image that follows, when the field names are similar to one another the system can successfully match the two.
+<br><img src="{{site.url}}{{site.baseurl}}/images/Security/default-mappings.png" alt="Field mapping example for pending mappings" width="85%">
+
+Nevertheless, it's a good idea to review the mappings and verify that they are correct and matched as expected. If you find a mapping that doesn't appear to be accurate, you can use the dropdown list as described in the [Pending field mappings](#pending-field-mappings) section above to correct the field mapping.  
+
+After completing the mappings, select the **Next** button in the lower-right corner of the screen. The **Set up alerts** page appears and displays settings for an alert trigger.
+
+## Step 3. Set up alerts
+
+At this stage, setting up alerts is optional for creating a new detector. Alerts can be configured at any time, including from the Findings window. This section describes the process for defining the alert conditions during creation of a detector. To see how to initiate creation of alerts from the Findings window, see [The findings list]({{site.url}}{{site.baseurl}}/security-analytics/usage/findings/#the-findings-list).
+
+To skip directly to generating findings from the detector, select the **Remove alert trigger** button and then the **Next** button in the lower-right corner of the screen. Review the detector's definition and then select the **Create** button in the lower-right corner of the screen. The detector is created.
+{: .tip }
+
+To set up an alert for the detector at this stage of detector creation, continue with the following steps:
 
 1. In the **Trigger name** box, enter a name for the trigger.
 1. To define rule matches for the alert, select security rules, severity levels, and tags.
-<br><img src="{{site.url}}{{site.baseurl}}/images/Security/alert_rules.png" alt="Rules used to define an alert">
+<img src="{{site.url}}{{site.baseurl}}/images/Security/alert_rules.png" alt="Rules used to define an alert">
 * Select one rule or multiple rules that will trigger the alert. Put the cursor in the **Rule names** box and type a name to search for it. To remove a rule name, select the **X** beside the name. To remove all rule names, select the **X** beside the dropdown menu's down arrow.
 <br><img src="{{site.url}}{{site.baseurl}}/images/Security/rule_name_delete.png" alt="Deletes all selected rules">
 * Select one or more rule severities as conditions for the alert.
 * Select from a list of tags to include as conditions for the alert.
 1. To define a notification for the alert, assign an alert severity, select a channel for the notification, and customize a message generated for the alert.
-<br><img src="{{site.url}}{{site.baseurl}}/images/Security/alert_notify.png" alt="Notification settings for the alert">
+<img src="{{site.url}}{{site.baseurl}}/images/Security/alert_notify.png" alt="Notification settings for the alert">
 * Assign a level of severity for the alert to give the recipient an indication of its urgency.
 * Select a channel for the notification. Examples include Slack, Chime, or email. Select the  **Manage channels** link to the right of the field to link the notification to a preferred channel.
 * Select the **Show notify message** label to expand message preferences. You can add a subject for the message and a note to inform recipients of the nature of the message.