Update 4.storage-service.md (#2161)

docs-2.0/1.introduction/3.nebula-graph-architecture/4.storage-service.md

@@ -124,11 +124,11 @@ In NebulaGraph, an edge corresponds to two key-value pairs on the hard disk. Whe
 
 ![partitioning by edge](https://docs-cdn.nebula-graph.com.cn/figures/edge-division.png)
 
-In this example, ScrVertex connects DstVertex via EdgeA, forming the path of `(SrcVertex)-[EdgeA]->(DstVertex)`. ScrVertex, DstVertex, and EdgeA will all be stored in Partition x and Partition y as four key-value pairs in the storage layer. Details are as follows:
+In this example, SrcVertex connects DstVertex via EdgeA, forming the path of `(SrcVertex)-[EdgeA]->(DstVertex)`. SrcVertex, DstVertex, and EdgeA will all be stored in Partition x and Partition y as four key-value pairs in the storage layer. Details are as follows:
 
 * The key value of SrcVertex is stored in Partition x. Key fields include Type, PartID(x), VID(Src), and TagID. SerializedValue, namely Value, refers to serialized vertex properties.
 
-* The first key value of EdgeA, namely EdgeA_Out, is stored in the same partition as the ScrVertex. Key fields include Type, PartID(x), VID(Src), EdgeType(+ means out-edge), Rank(0), VID(Dst), and PlaceHolder. SerializedValue, namely Value, refers to serialized edge properties.
+* The first key value of EdgeA, namely EdgeA_Out, is stored in the same partition as the SrcVertex. Key fields include Type, PartID(x), VID(Src), EdgeType(+ means out-edge), Rank(0), VID(Dst), and PlaceHolder. SerializedValue, namely Value, refers to serialized edge properties.
 
 * The key value of DstVertex is stored in Partition y. Key fields include Type, PartID(y), VID(Dst), and TagID. SerializedValue, namely Value, refers to serialized vertex properties.