5.9.2 Edge File

Each line in an edge file is a record that describes an edge of the property graph. A record can describe one key-value property of an edge, thus multiple records are used to describe an edge with multiple properties.

A record contains nine fields separated by commas. Each record must contain eight commas to delimit all fields, whether or not they have values:

edge_ID, source_vertex_ID, destination_vertex_ID, edge_label, key_name, value_type, value, value, value

The following table describes the fields composing an edge file record.

Table 5-1 Edge File Record Format

Field Number	Name	Description
1	edge_ID	An integer that uniquely identifies the edge
2	source_vertex_ID	The vertex_ID of the outgoing tail of the edge.
3	destination_vertex_ID	The vertex_ID of the incoming head of the edge.
4	edge_label	The encoded label of the edge, which describes the relationship between the two vertices
5	key_name	The encoded name of the key in a key-value pair If the edge has no properties, then enter a space (%20). This example describes edge 100 with no properties: 100,1,2,likes,%20,,,,
6	value_type	An integer that represents the data type of the value in the key-value pair: 1 String 2 Integer 3 Float 4 Double 5 Timestamp (date) 6 Boolean 7 Long integer 8 Short integer 9 Byte 10 Char 20 Spatial 101 Serializable Java object
7	value	The encoded, nonnull value of key_name when it is neither numeric nor timestamp (date)
8	value	The encoded, nonnull value of key_name when it is numeric
9	value	The encoded, nonnull value of key_name when it is a timestamp (date) Use the Java SimpleDateFormat class to identify the format of the date. This example describes the date format of 2015-03-26Th00:00:00.000-05:00: SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSXXX"); encode(sdf.format((java.util.Date) value));

Required Grouping of Edges: An edge can have multiple properties, and the edge file includes a record (represented by a single line of text in the flat file) for each combination of an edge ID and a property for that edge. In the edge file, all records for each edge must be grouped together (that is, not have any intervening records for other edges. You can accomplish this any way you want, but a convenient way is to sort the edge file records in ascending (or descending) order by edge ID. (Note, however, an edge file is not required to have all records sorted by edge ID; this is merely one way to achieve the grouping requirement.)

When building an edge file in Oracle flat file format, it is important to verify that the edge property name and value fields are correctly encoded (see especially Encoding Special Characters). To simplify the encoding, you can use the OraclePropertyGraphUtils.escape Java API.

You can use the OraclePropertyGraphUtils.outputEdgeRecord(os, eid, svid, dvid, label, key, value) utility method to serialize an edge record directly in Oracle flat file format. With this method, you no longer need to worry about encoding of special characters. The method writes a new line of text in the given output stream describing the key/value property of the given edge identified by eid.

Example 5-24 Using OraclePropertyGraphUtils.outputEdgeRecord

This example uses OraclePropertyGraphUtils.outputEdgeRecord to write two new lines for edge 100 between vertices 1 and 2 with label friendOf.

OutputStream os = new FileOutputStream("./example.ope");
int sinceYear = 2009;
long eid = 100;
long svid = 1;
long dvid = 2;
OraclePropertyGraphUtils.outputEdgeRecord(os, eid, svid, dvid, "friendOf", "since (year)", sinceYear);
OraclePropertyGraphUtils.outputEdgeRecord(os, eid, svid, dvid, "friendOf", "weight", 1);
os.flush();
os.close();

The first line in the generated output file describes the property “since (year)" with value 2009, and the second line and the next line sets the edge weight to 1.

% cat example.ope
100,1,2,friendOf,since%20(year),2,,2009,
100,1,2,friendOf,weight,2,,1,