diff --git a/dbterd/adapters/targets/mermaid/mermaid_test_relationship.py b/dbterd/adapters/targets/mermaid/mermaid_test_relationship.py
index 8d86368..feb17b6 100644
--- a/dbterd/adapters/targets/mermaid/mermaid_test_relationship.py
+++ b/dbterd/adapters/targets/mermaid/mermaid_test_relationship.py
@@ -18,10 +18,28 @@ def run(manifest, catalog, **kwargs):
 
 
 def replace_column_name(column_name: str) -> str:
+    """Replace column names containing special characters.
+    To prevent mermaid from not being able to render column names that may contain special characters.
+
+    Args:
+        column_name (str): column name
+
+    Returns:
+        str: Column name with special characters substituted
+    """
     return column_name.replace(" ", "-").replace(".", "__")
 
 
 def match_complex_column_type(column_type: str) -> Optional[str]:
+    """Returns the root type from nested complex types.
+    As an example, if the input is `Struct<field1 string, field2 string>`, return `Struct`.
+
+    Args:
+        column_type (str): column type
+
+    Returns:
+        Optional[str]: Returns the root type if the input type is a nested complex type, otherwise returns `None` for primitive types
+    """
     pattern = r"(\w+)<(\w+\s+\w+(\s*,\s*\w+\s+\w+)*)>"
     match = re.match(pattern, column_type)
     if match:
@@ -31,6 +49,15 @@ def match_complex_column_type(column_type: str) -> Optional[str]:
 
 
 def replace_column_type(column_type: str) -> str:
+    """If the type string contains special characters that cannot be drawn by mermaid, replace them with strings that can be drawn.
+    If the type string contains a nested complex type, omit it to make it easier to read.
+
+    Args:
+        column_type (str): column type
+
+    Returns:
+        str: Type of column with special characters are substituted or omitted
+    """
     # Some specific DWHs may have types that cannot be drawn in mermaid, such as `Struct<first_name string, last_name string>`.
     # These types may be nested and can be very long, so omit them
     complex_column_type = match_complex_column_type(column_type)