Add comments about Filter and Functions.

docs/README.md

 ## Documents
-[![cn doc](https://img.shields.io/badge/document-中文-blue.svg)](README_ZH.md)
 
+  * [SkyWalking Platform Overview](en/OAP/README.md)
+  * Use application agents
+  * Use service mesh probes
+  * Deploy OAP backend
+  
+We will begin to build our new documents for our new 6 version. Below it is 5.x document, wait for reformat.  
+----------------------------  
+  
   * Getting Started
     * [Quick start](en/Quick-start.md)
     * [Install javaagent](en/Deploy-skywalking-agent.md)
@@ -11,7 +18,6 @@
         * [Trace Spring beans](en/agent-optional-plugins/Spring-bean-plugins.md)
         * [Trace Oracle and Resin](en/agent-optional-plugins/Oracle-Resin-plugins.md)
         * [[**Incubating**] Filter traces through custom services](../apm-sniffer/optional-plugins/trace-ignore-plugin/README.md)
-  * [Architecture Design](en/Architecture.md)
   * Advanced Features
     * [Override settings through System.properties](en/Setting-override.md)
     * [Direct uplink and disable naming discovery](en/Direct-uplink.md)

docs/en/Architecture.md

-# Architecture Design
-## Background
-For APM, agent or SDKs are just the technical details about how to instrument the libs. 
-Manual or auto are nothing about the architecture, so in this document, we will consider them as a client lib only.
-
-<img src="https://skywalkingtest.github.io/page-resources/5.0/architecture.png"/>
-
-## Basic Principles
-The basic design principles of SkyWalking architecture are **easy to maintain, controllable and streaming**. 
-
-In order to achieve these goals, SkyWalking backend provides the following designs.
-1. Modulization design.
-1. Multiple connection ways for client side.
-1. Collector cluster discovery mechanism
-1. Streaming mode.
-1. Swtichable storage implementors.
-
-## Modulization
-SkyWalking collector is based on pure **modulization design**. End user can switch or assemble the collector features by their
-own requirements.
-
-### Module
-
-Module defines a collection of features, which could include techenical implementors(such as: gRPC/Jetty server managements), 
-trace analysis(such as: trace segment or zipkin span parser), or aggregation feature. Totally decided by the module definition
-and its implementors.
-
-Each module could define their services in Java Interface, 
-and every providers of the module must provide implementors for these services. 
-And the provider should define the dependency modules based its own implementation. 
-So it means, even two different implementors of the module, could depend different modules.
-
-Also the collector modulization core checks the startup sequences, if cycle dependency or dependency not found occurs, 
-collector should be terminated by core.
-
-The collector startup all modules, which are decleared in `application.yml`. 
-In this yaml file
-- Root level is the module name, such as `cluster`, `naming`
-- Secondary level is the implementor name of the module, such as `zookeeper` is the `cluster` module
-- Third level are attributes of the implementors. Such as `hostPort` and `sessionTimeout` are required attributes of `zookepper`.
-
-_The example part of the yaml definitation_
-```yml
-cluster:
-  zookeeper:
-    hostPort: localhost:2181
-    sessionTimeout: 100000
-naming:
-  jetty:
-    #OS real network IP(binding required), for agent to find collector cluster
-    host: localhost
-    port: 10800
-    contextPath: /
-```
-
-## Multiple connection ways
-First of all, the collector provides two types of connections, also two protocols(HTTP and gRPC). These two are
-1. Naming service in HTTP, which returns the all available collectors in the backend cluster.
-1. Uplink service in gRPC(primary in SkyWalking native agents) and HTTP, which uplinks traces and metrics to collector.
-Each client will only send monitoring data(traces and metrics) to a single collector. Attempt to connect other if the connected one offline.
-
-Such as in SkyWalking Java agent
-1. `collector.servers` means the naming service, which maps to `naming/jetty/ip:port` of collector, in HTTP. 
-1. `collector.direct_servers` means setting Uplink service directly, and using gRPC to send monitoring data.
-
-
-_Example of the process flow between client lib and collector cluster_
-```
-         Client lib                         Collector1             Collector2              Collector3
- (Set collector.servers=Collector2)              (Collector 1,2,3 constitute the cluster)
-             |
-             +-----------> naming service ---------------------------->|
-                                                                       |
-             |<------- receive gRPC IP:Port(s) of Collector 1,2,3---<--|
-             |
-             |Select a random gRPC service
-             |For example collector 3
-             |
-             |------------------------->Uplink gRPC service----------------------------------->|
-```
-
-
-## Collector Cluster Discovery
-When collectors are running in cluster mode, collector must discovery each other in some way. In default, SkyWalking uses
-Zookeeper to coordinate and as register center for instance discovery.
-
-Through the above section([Multiple connection ways](#multiple-connection-ways)), client lib will not use the Zookeeper to find cluster. And we suggest the client shouldn't do it in that way. Because the cluster discovery mechanism is switchable, 
-provided by modulization core. Relying on that breaks the switchable capability.
-
-We hope the community provides more implementor to do cluster discovery, such as Eureka, Consul, Kubernate.
-
-
-## Streaming Mode
-Streaming mode likes a lightweight storm/spark implementation, which allows using APIs to build streaming process graph(DAG),
-and the input/output data contracts of each node.
-
-New module can find and extend the existed process graph. 
-
-There are three cases in processing
-1. Synchronizing process. Tranditional method invocation.
-1. Asynchronizing process, a.k.a batch process based on Queue buffer.
-1. Remote process. Aggregate metrices across collector. In that way, selector is defined in node to decide 
-how to find the collector in cluster. (HashCode, Rolling, ForeverFirst are the three ways supported)
-
-By having these features, collector cluster runs like as a streaming net, to aggregate the metrics and don't rely on the
-storage implementor to support writing the same metric id concurrently.
-
-## Swtichable Storage Implementors
-Because streaming mode takes care of the concurrent, storage implementor responsibilities are provide high speed write,
-and group query.
-
-Right now, we supported ElasticSearch as primary implementor, H2 for preview, and MySQL Relational Database cluster managed
-by ShardingShpere project. 
-
-# Web UI
-Besides the principles in collector design, UI is another core component in SkyWalking. It is based on React, Antd and Zuul
-proxy to provide collector cluster discovery, query dispatch and visualziation.
-
-Web UI shares the similiar process flow as client's `1.naming then 2.uplink` mechanism in [Multiple connection ways](#multiple-connection-ways) section. The only difference is that, replace the uplink with GraphQL query protocol in HTTP binding at the host and port under `ui/jetty/` in yaml definition(default:`localhost:12800`).
-

docs/en/OAP/README.md

@@ -170,20 +170,24 @@ including auto instrument agents(like Java, .NET), OpenCensus SkyWalking exporte
 | detectPoint | Represent where is the relation detected. Values: client, server, proxy. | yes | enum|
 
 #### Filter
-Use filter to build the conditions for the value of fields, by using field name and expression.
+Use filter to build the conditions for the value of fields, by using field name and expression. 
+
+The expressions support to link by `and`, `or` and `(...)`. 
+The OPs support `=`, `!=`, `>`, `<`, `in (v1, v2, ...`, `like "%..."`, with type detection based of field type. Trigger compile
+ or code generation error if incompatible. 
 
 #### Aggregation Function
-The default functions are provided by SkyWalking OAP core, and could implement more.
+The default functions are provided by SkyWalking OAP core, and could implement more. 
 
 Provided functions
-- `avg`
-- `p99`
-- `p90`
-- `p75`
-- `p50`
-- `percent`
-- `histogram`
-- `sum`
+- `avg()`. The average value. The field type must be number.
+- `p99()`. The 99% of the given values should be greater or equal. The field type must be number.
+- `p90()`. The 90% of the given values should be greater or equal. The field type must be number.
+- `p75()`. The 75% of the given values should be greater or equal. The field type must be number.
+- `p50()`. The 75% of the given values should be greater or equal. The field type must be number.
+- `percent()`. The percentage of selected by filter in the whole given data. No type requirement.
+- `histogram(start, step)`. Group the given value by the given step, begin with the start value.
+- `sum()`. The sum number of selected by filter. No type requirement.
 
 #### Metric name
 The metric name for storage implementor, alarm and query modules. The type inference supported by core.