Centralize attributes definition (open-telemetry#722)

* Centralize attributes definition Signed-off-by: Bogdan Drutu <[email protected]> * Update specification/common/common.md Co-authored-by: Christian Neumüller <[email protected]> * Update specification/common/common.md Co-authored-by: Christian Neumüller <[email protected]> * Update specification/common/common.md Co-authored-by: Christian Neumüller <[email protected]> * Update specification/common/common.md Co-authored-by: Christian Neumüller <[email protected]> * Update specification/common/common.md Co-authored-by: Christian Neumüller <[email protected]> * Update specification/common/common.md Co-authored-by: Christian Neumüller <[email protected]> * Update specification/overview.md Co-authored-by: Christian Neumüller <[email protected]> Co-authored-by: Christian Neumüller <[email protected]>
kaiyan-sheng · Nov 16, 2023 · 4f5831c · 4f5831c
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+# Common specification concepts
+
+<details>
+<summary>
+Table of Contents
+</summary>
+
+- [Attributes](#attribute)
+
+</details>
+
+## Attributes
+
+Attributes are a list of zero or more key-value pairs. An `Attribute` MUST have the following properties:
+
+- The attribute key, which MUST be a non-`null` and non-empty string.
+- The attribute value, which is either:
+  - A primitive type: string, boolean, double precision floating point (IEEE 754-1985) or signed 64 bit integer.
+  - An array of primitive type values. The array MUST be homogeneous,
+    i.e. it MUST NOT contain values of different types. For protocols that do
+    not natively support array values such values SHOULD be represented as JSON strings.
+
+`null` values within arrays MUST be preserved as-is (i.e., passed on to span
+processors / exporters as `null`). If exporters do not support exporting `null`
+values, they MAY replace those values by 0, `false`, or empty strings.
+This is required for map/dictionary structures represented as two arrays with
+indices that are kept in sync (e.g., two attributes `header_keys` and `header_values`,
+both containing an array of strings to represent a mapping
+`header_keys[i] -> header_values[i]`).