[GitHub] [skywalking-banyandb] hanahmily commented on a diff in pull request #198: Add data-model.md to explian objectes in API

[GitBox <gi...@apache.org>]

hanahmily commented on code in PR #198:
URL: https://github.com/apache/skywalking-banyandb/pull/198#discussion_r1008780867


##########
docs/concept/data-model.md:
##########
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+# Data Model
+
+This chapter introduces BanyanDB's data models and covers the following:
+
+* the high-level data organization
+* data model
+* data retrieval
+
+You can also find [examples](../crud/) of how to interact with BanyanDB using [bydbctl](../clients.md#command-line), how to create and drop groups, or how to create, read, update and drop streams/measures.
+
+## Structure of BanyanDB
+
+The hierarchy that data is organized into **streams**, **measures** and **properties** in groups.
+
+![Structure of BanyanDB](../assets/structure.png)
+
+### Measures
+
+BanyanDB lets you define a measure as follows:
+
+```yaml
+metadata:
+  name: service_cpm_minute
+  group: sw_metric
+tag_families:
+- name: default
+  tags:
+  - name: id
+    type: TAG_TYPE_ID
+  - name: entity_id
+    type: TAG_TYPE_STRING
+fields:
+- name: total
+  field_type: FIELD_TYPE_INT
+  encoding_method: ENCODING_METHOD_GORILLA
+  compression_method: COMPRESSION_METHOD_ZSTD
+- name: value
+  field_type: FIELD_TYPE_INT
+  encoding_method: ENCODING_METHOD_GORILLA
+  compression_method: COMPRESSION_METHOD_ZSTD
+entity:
+  tag_names:
+  - entity_id
+interval: 1m
+```
+
+`Measure` consists of a sequence of data points. Each data point contains tags and fields.
+
+`Tags` are key-value pairs. The database engine can index tag values by referring to the index rules and rule bindings, confining the query to filtering data points based on tags bound to an index rule.
+
+`Tags` are grouped into unique `tag_families` which are the logical and physical grouping of tags.
+
+`Measure` supports the following tag types:
+
+* **STRING** : Text
+* **INT** : 64 bits long integer
+* **STRING_ARRAY** : A group of strings
+* **INT_ARRAY** : A group of integers
+* **DATA_BINARY** : Raw binary
+* **ID** : Identity of a data point in a measure. If several data points come with an identical ID typed tag, the last write wins according to the `timestamp`.
+
+A group of selected tags composite an `entity` that points out a specific time series the data point belongs to. The database engine has capacities to encode and compress values in the same time series. Users should select appropriate tag combinations to optimize the data size. Another role of `entity` is the sharding key of data points, determining how to fragment data between shards.
+
+`Fields` are also key-value pairs like tags. But the value of each field is the actual value of a single data point. The database engine would encode and compress the field's values in the same time series. The query operation is forbidden to filter data points based on a field's value. You could apply aggregation
+functions to them.
+
+`Measure` supports the following fields types:
+
+* **STRING** : Text
+* **INT** : 64 bits long integer
+* **DATA_BINARY** : Raw binary
+
+`Measure` supports the following encoding methods:
+
+* **GORILLA** : GORILLA encoding is lossless. It is more suitable for a numerical sequence with similar values and is not recommended for sequence data with large fluctuations.
+
+`Measure` supports the types of the following fields:
+
+* **ZSTD** : Zstandard is a real-time compression algorithm, that provides high compression ratios. It offers a very wide range of compression/speed trade-offs, while being backed by a very fast decoder. For BanyanDB focus on speed.
+
+Another option named `interval` plays a critical role in encoding. It indicates the time range between two adjacent data points in a time series and implies that all data points belonging to the same time series are distributed based on a fixed interval. A better practice for the naming measure is to append the interval literal to the tail, for example, `service_cpm_minute`. It's a parameter of `GORILLA` encoding method.
+
+[Measure Registration Operations](../api-reference.md#measureregistryservice)
+
+#### TopNAggregation

Review Comment:
   @lujiajing1126 Would you please check this section?



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