Hello and STEP File Question

Hello all,

I am new to this forum and am trying to learn the STEP File format. I hope someone here can help. I am trying to understand the B_SPLINE_CURVE_WITH_KNOTS STEP Entity of the form ".POLYLINE_FORM.". I am building my own parser with Java and am not sure about the image the input STEP File is defining(maybe cylinder?).Below is a sample of the area of the STEP File I am speaking of:
...

#2981=ADVANCED_FACE('F24',(#2980),#2934,.F.);
#2980=FACE_OUTER_BOUND('F24',#2979,.T.);
#2979=EDGE_LOOP('F24',(#2943,#2960,#2961,#2978));
#2943=ORIENTED_EDGE('E73',*,*,#2942,.F.);
#2942=EDGE_CURVE('E73',#2936,#2938,#2941,.T.);
#2936=VERTEX_POINT('V50',#2935);
#2938=VERTEX_POINT('V47',#2937);
#2941=B_SPLINE_CURVE_WITH_KNOTS('E73',1,(#2939,#2940),
.POLYLINE_FORM.,.F.,.U.,(2,2),(0.0,0.271863842075010),
.UNSPECIFIED.);

#2959=EDGE_CURVE('E74',#2936,#2936,#2958,.T.);
#2960=ORIENTED_EDGE('E74',*,*,#2959,.F.);
#2936=VERTEX_POINT('V50',#2935);
#2958=(BOUNDED_CURVE()B_SPLINE_CURVE(2,(#2944,#2945,#2946,#2947,
#2948,#2949,#2950),.CIRCULAR_ARC.,.T.,.U.)
B_SPLINE_CURVE_WITH_KNOTS((3,2,2,3),(0.0,0.382356173618420,0.764712347236830,1.147068520855200),.UNSPECIFIED.)CURVE()
GEOMETRIC_REPRESENTATION_ITEM()RATIONAL_B_SPLINE_CURVE((1.0,
0.500000000000000,1.0,0.500000000000000,1.0,0.500000000000000,1.0)

...

The above "line" entity (#2941) is repeated again for another "circle" entity (similar to #2958). Should this "line" be repeated around the "circles" such that a cylinder is created?

Sorry if this post is a bit unclear, it is hard to describe my issue without pictures. Also if anyone can point me to a STEP/IGES File explaination/FAQ page that would be great.

Thank you