Convert ECS doc from MD to asciidoc guide: initial setup (#266)

* ECS doc conversion from md to asciidoc

* Add back uc-header file

* New asciidoc files

docs/contributing.asciidoc

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+[[ecs-contributing]]
+== Contributing to {ecs}
+
+All information related to ECS is versioned in the https://github.com/elastic/ecs[elastic/ecs] repository. All
+changes to ECS happen through Pull Requests submitted through Git.
+
+See the https://github.com/elastic/ecs/blob/master/CONTRIBUTING.md[Contribution Guidelines].
+

docs/conventions.asciidoc

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+//[[ecs-conventions]]
+== {ecs} Conventions
+
+{ecs} is most effective when you understand and follow conventions.
+
+[float]
+=== Multi-fields text indexing
+
+Elasticsearch can index text using:
+
+* *Text.* Text indexing allows for full text search, or searching arbitrary words that
+  are part of the field. 
+  See https://www.elastic.co/guide/en/elasticsearch/reference/current/text.html[Text datatype]
+  in the {es} Reference Guide.
+* *Keywords.* Keyword indexing offers faster exact match filtering and prefix search,
+  and makes aggregations (for Kibana visualizations) possible.
+  See the {es} Reference Guide for more information on 
+  https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-term-query.html[exact match filtering],
+  https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-prefix-query.html[prefix search], or 
+  https://www.elastic.co/guide/en/elasticsearch/reference/current/search-aggregations.html[aggregations].
+
+
+[float]
+==== Default Elasticsearch convention
+
+Unless your index mapping or index template specifies otherwise
+(as the ECS index template does),
+Elasticsearch indexes text field as `text` at the canonical field name,
+and indexes a second time as `keyword`, nested in a multi-field.
+
+Default Elasticsearch convention:
+
+* Canonical field: `myfield` is `text`
+* Multi-field: `myfield.keyword` is `keyword`
+
+[float]
+==== ECS multi-field convention for text
+
+For monitoring use cases, `keyword` indexing is needed almost exclusively, with
+full text search on very few fields. Given this premise, ECS defaults
+all text indexing to `keyword` at the top level (with very few exceptions).
+Any use case that requires full text search indexing on additional fields
+https://www.elastic.co/guide/en/elasticsearch/reference/current/multi-fields.html[multi-field].
+for full text search. Doing so does not conflict with ECS,
+as the canonical field name will remain `keyword` indexed.
+
+ECS multi-field convention for text:
+
+* Canonical field: `myfield` is `keyword`
+* Multi-field: `myfield.text` is `text`
+
+[float]
+==== Exceptions
+
+The only exceptions to this convention are fields `message` and `error.message`,
+which are indexed for full text search only, with no multi-field.
+These two fields don't follow the new convention because they are deemed too big
+of a breaking change with these two widely used fields in Beats.
+
+Any future field that will be indexed for full text search in ECS will however
+follow the multi-field convention where `text` indexing is nested in the multi-field.
+
+[float]
+=== IDs and most codes are keywords, not integers
+
+Despite the fact that IDs and codes (e.g. error codes) are often integers,
+this is not always the case.
+Since we want to make it possible to map as many systems and data sources
+to ECS as possible, we default to using the `keyword` type for IDs and codes.
+
+Some specific kinds of codes are always integers, like HTTP status codes.
+If those have a specific corresponding specific field (as HTTP status does),
+its type can safely be an integer type.
+But generic field like `error.code` cannot have this guarantee, and are therefore `keyword`.
+
+

docs/fields.asciidoc

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+[[ecs-fields]]
+== {ecs} Fields
+
+// Add a list of field types w/ brief description so user can get a 
+// sense of what we're offering without having to scroll.
+
+// Pull in generated field content using `include` statements
+
+[cols="<,<",options="header",]
+|=======================================================================
+| Fields  | Description  
+| <<ecs-base,Base>> | The base set contains all fields which are on the top level.
+ These fields are common across all types of events.
+| <<ecs-agent,Agent>> | The agent fields contain data about the 
+agent/client/shipper that created the event.
+| <<ecs-cloud,Cloud>> | Fields related to the cloud or infrastructure the events are
+ coming from.
+| <<ecs-container,Container>> | Container fields are used for meta information about the specific container that
+is the source of information. These fields help correlate data based containers
+from any runtime.
+| <<ecs-destination,Destination>> | Destination fields describe details about the destination of a packet/event.
+| <<ecs-device,Device>> | Device fields are used to provide additional information 
+about the device that is the source of the information. This could be a firewall, network device, etc.
+| <<ecs-ecs,ECS>> | Meta-information specific to ECS.
+| <<ecs-error,Error>> | These fields can represent errors of any kind. Use them for errors that happen
+while fetching events or in cases where the event itself contains an error.
+| <<ecs-event,Event>> | The event fields are used for context information about the data itself.
+| <<ecs-file,File>> | File fields provide details about each file.
+| <<ecs-geo,Geo>> | Geo fields can carry data about a specific location related to 
+an event or geo information derived from an IP field.
+The `geo` fields are expected to be nested at: `destination.geo`, `device.geo`, `host.geo`, `source.geo`.
+| <<ecs-host,Host>> | Host fields provide information related to a host. A host can be a physical
+machine, a virtual machine, or a Docker container.
+| <<ecs-log,Log>> | Fields which are specific to log events.
+| <<ecs-network,Network>> | Fields related to network data.
+| <<ecs-organization,Organization>> | The organization fields enrich data with 
+  information about the company or entity the data is associated with. These fields help
+  you arrange or filter data stored in an index by one or multiple organizations.
+| <<ecs-os,Operating System>> | The OS fields contain information about the operating system.
+| <<ecs-process,Process>> | These fields contain information about a process. These fields can help you
+correlate metrics information with a process id/name from a log message.  The
+`process.pid` often stays in the metric itself and is copied to the global field
+for correlation.
+| <<ecs-service,Service>> | The service fields describe the service for or from which the data was
+collected. These fields help you find and correlate logs for a specific service
+and version.
+| <<ecs-source,Source>> | Source fields describe details about the destination of a packet/event.
+| <<ecs-url,URL>> | URL fields provide a complete URL, with scheme, host, and path.
+| <<ecs-user,User>> | The user fields describe information about the user 
+ that is relevant to the event. Fields can have one entry or multiple entries. 
+ If a user has more than one id, provide an array that includes all of them.
+|=======================================================================
+
+include::fields-gen.asciidoc[]
+
+
+

docs/glossary.asciidoc

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+//[[ecs-glossary]]
+== Glossary of {ecs} Terms
+
+[[glossary-ecs]] 
+ECS ::
+
+Elastic Common Schema. A common set of document fields, field names, and their respective entity
+relationships to be used in the storage of log messages and other data in
+Elasticsearch.
+
+
+

docs/guidelines.asciidoc

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+//[[ecs-guidelines]]
+== Guidelines and Best Practices
+
+The {ecs} schema serves best when you follow schema guidelines and best
+practices.
+
+[float]
+=== General guidelines
+
+* The document MUST have the `@timestamp` field.
+* Use the https://www.elastic.co/guide/en/elasticsearch/reference/current/mapping-types.html[data type]
+  defined for an ECS field.
+* Use the `ecs.version` field to define which version of ECS is used.
+* Map as many fields as possible to ECS.
+* TBD: Include guidelines on when people should contribute to the spec. Link to Contributing.
+
+[float]
+==== Guidelines for writing fields
+
+* All fields must be lower case
+* Combine words using underscore
+* No special characters except `_`
+
+[float]
+==== Guidelines for naming fields
+
+* *Present tense.* Use present tense unless field describes historical information.
+* *Singular or plural.* Use singular and plural names properly to reflect the field content. For example, use `requests_per_sec` rather than `request_per_sec`.
+* *General to specific.* Organise the prefixes from general to specific to allow grouping fields into objects with a prefix like `host.*`.
+* *Avoid repetition.* Avoid stuttering of words. If part of the field name is already in the prefix, do not repeat it. Example: `host.host_ip` should be `host.ip`.
+* *Use prefixes.* Fields must be prefixed except for the base fields. For example all `host` fields are prefixed with `host.`. See `dot` notation in FAQ for more details.
+* *Avoid abbreviations when possible*. A few exceptions like `ip` exist.
+

docs/index.asciidoc

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+:doctype: book
+:ecs: ECS
+
+
+include::{asciidoc-dir}/../../shared/versions.asciidoc[]
+include::{asciidoc-dir}/../../shared/attributes.asciidoc[]
+
+[[ecs-reference]]
+== Elastic Common Schema (ECS) Reference
+
+beta[]
+
+The Elastic Common Schema (ECS) defines a common set of fields for
+ingesting data into Elasticsearch. A common schema helps you correlate
+data from sources like logs and metrics or IT operations
+analytics and security analytics.
+
+ECS is still under development and backward compatibility is not guaranteed. Any
+feedback on the general structure, missing fields, or existing fields is appreciated.
+For contributions please read the  https://github.com/elastic/ecs/blob/master/CONTRIBUTING.md[Contribution Guidelines].
+
+[float]
+[[versions]]
+=== Versions
+
+The master branch of this repository should never be considered an
+official release of ECS. You can browse https://github.com/elastic/ecs/releases[official releases] of ECS.
+
+Please note that when the README.md file and other generated files
+(like schema.csv and template.json) are not in agreement,
+the README.md should be considered the official spec.
+The other two files are simply provided as a convenience, and may not always be
+fully up to date.
+
+/////
+Working TOC
+
+ECS Intro
+  Versions
+  MINI TOC???
+Fields (generated)
+  Base
+  Agent
+  Cloud
+  ETC
+* Use Case header = Use Cases (generated)
+* Implementing
+* About (FAQs)
+* Contributing
+* GLOSSARY? 
+
+* Mike's stuff (https://docs.google.com/document/d/1srylXQDgO0z5rbwho1o8nKIxr9icTTl_nXZGYbElxYs/edit#heading=h.y1xeds3o3jae)
+
+ECS Definitions and Entity Relationships
+** ECS data model
+** Definitions
+** Top-Level Namespaces/Objects
+** Reusable Namespaces/Objects
+** Assets and Asset Lists
+** Pseudonymized and Anonymized Data in ECS
+** Threat and Vulnerability Data in ECS
+** Revisit inbound, outbound bytes/packets
+
+
+//////
+
+include::fields.asciidoc[]
+include::conventions.asciidoc[]
+include::guidelines.asciidoc[]
+include::use-cases.asciidoc[]
+include::contributing.asciidoc[]
+include::glossary.asciidoc[]
+

docs/use-cases.asciidoc

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+[[ecs-use-cases]]
+== Use Cases
+
+The power and versatility of {ecs} is best illustrated through use cases. 
+
+NOTE: Some use cases contain ECS fields and additional fields which are not
+in ECS to describe the full use case. The fields which are not in ECS are in
+italic.
+
+ * https://github.com/elastic/ecs/blob/master/use-cases/apm.md[APM]
+ * https://github.com/elastic/ecs/blob/master/use-cases/auditbeat.md[Auditbeat]
+ * https://github.com/elastic/ecs/blob/master/use-cases/beats.md[Beats]
+ * https://github.com/elastic/ecs/blob/master/use-cases/filebeat-apache-access.md[Filebeat Apache]
+ * https://github.com/elastic/ecs/blob/master/use-cases/kubernetes.md[Kubernetes]
+ * https://github.com/elastic/ecs/blob/master/use-cases/logging.md[Logging]
+ * https://github.com/elastic/ecs/blob/master/use-cases/metricbeat.md[Metricbeat]
+ * https://github.com/elastic/ecs/blob/master/use-cases/tls.md[TLS]
+ * https://github.com/elastic/ecs/blob/master/use-cases/web-logs.md[Parsing web server logs]
+
+We welcome https://github.com/elastic/ecs/blob/master/CONTRIBUTING.md[contributions] of additional ECS uses cases. 
+
+
+