在IFC中，聚合关系IfcRelAggregates 是一种特殊的IfcRelDecomposes组成/分解（或整体/部分）关系。“整体”依赖于“部分”的定义，“部分”依赖于“整体”的存在，必须在应用程序里建立起依赖关系。
在聚合关系下，物体的整体形状是各个部分形状的总和。如屋顶是屋顶元素的聚合，包括屋顶板，椽子，桁梁等，屋顶的几何形状是各个屋顶元素几何形状组成。
IfcRelAggregates主要包括：
（1）RelatingObject："整体/部分"关系中“整体”。
（2）RelatedObjects："整体/部分"关系中“部分”。
IFC文件的内容如下：
1 #103= IFCPROJECT('1o0c33arXF9AEePDXPKItb',#42,'Project Number',$,$,'Project Name','Project Status',(#95),#90); 2 #118= IFCBUILDING('1o0c33arXF9AEePDXPKIta',#42,'',$,$,#33,$,'',.ELEMENT.,$,$,#114); 3 #131= IFCBUILDINGSTOREY('1o0c33arXF9AEePDYchjCY',#42,'Ground Floor',$,$,#129,$,'Ground Floor',.ELEMENT.,0.); 4 #137= IFCBUILDINGSTOREY('1o0c33arXF9AEePDYchj2Z',#42,'Roof',$,$,#136,$,'Roof',.ELEMENT.,2500.); 5 #177= IFCSPACE('3w0zWKm7n8SB1qbfwUzt0U',#42,'1 - Living room',$,$,#140,#172,'Living room',.ELEMENT.,.SPACE.,$); 6 #323= IFCSPACE('3w0zWKm7n8SB1qbfwUzt0J',#42,'2 - Bedroom',$,$,#309,#320,'Bedroom',.ELEMENT.,.SPACE.,$); 7 #421= IFCSPACE('3w0zWKm7n8SB1qbfwUzt0G',#42,'3 - Entrance hall',$,$,#407,#418,'Entrance hall',.ELEMENT.,.SPACE.,$); 8 #531= IFCSPACE('09J5N7xMHBfQZeQGAEMota',#42,'4 - Roof',$,$,#505,#528,'Roof',.ELEMENT.,.SPACE.,$); 9 #82887= IFCSITE('1o0c33arXF9AEePDXPKItd',#42,'Default',$,'',#82886,$,$,.ELEMENT.,(51,30,0,549316),(0,-7,-34,-450321),0.,$,$); 10 11 #83051= IFCRELAGGREGATES('3ccjyPAoj5dB6yvuLFhu$6',#42,$,$,#103,(#82887)); 12 #83055= IFCRELAGGREGATES('1s70IU8qzCLwjTi8v7zc07',#42,$,$,#82887,(#118)); 13 #83059= IFCRELAGGREGATES('3Zu5Bv0LOHrPC100A6FoQQ',#42,$,$,#131,(#177,#323,#421)); 14 #83065= IFCRELAGGREGATES('15Z0v90RiHrPC200A6FoKR',#42,$,$,#137,(#531)); 15 #83069= IFCRELAGGREGATES('2$1LAsj$T3CPRLiPj39tWH',#42,$,$,#118,(#131,#137));
（1）#83051（IfcRelAggregates）表示聚合关系，#103（项目，IfcProject）由#82887（场地，IfcSite）组成。
（2）#83055（IfcRelAggregates）表示聚合关系，#82887（场地，IfcSite）由#118（建筑，IfcBuilding）组成。
（3）#83069（IfcRelAggregates）表示聚合关系，#118（建筑，IfcBuilding）由#131（楼层，IfcBuildingStorey）#137（楼层，IfcBuildingStorey）组成。
（4）#83059（IfcRelAggregates）表示聚合关系，#131（楼层，IfcBuildingStorey）由#177（IfcSpace）, #323（IfcSpace），#421（IfcSpace）组成。
（5）#83065（IfcRelAggregates）表示聚合关系，#137（楼层，IfcBuildingStorey）由#531（IfcSpace）组成。
IFC文件的内容如下：
1 #2375= IFCCURTAINWALL('3cUkl32yn9qRSPvBJVyW_P',#42,'Curtain Wall:Curtain_Wall-Exterior_Glazing:285582',$,'Curtain Wall:Curtain_Wall-Exterior_Glazing:29096',#2374,$,'285582',$); 2 #2470= IFCPLATE('3cUkl32yn9qRSPvBJVyW_O',#42,'System Panel:Glazed:285583',$,'Glazed',#2468,#2458,'285583',.NOTDEFINED.); 3 #2628= IFCPLATE('3cUkl32yn9qRSPvBJVyW_5',#42,'System Panel:Glazed:285586',$,'Glazed',#2627,#2617,'285586',.NOTDEFINED.); 4 #2730= IFCPLATE('3cUkl32yn9qRSPvBJVyW_3',#42,'System Panel:Glazed:285588',$,'Glazed',#2729,#2719,'285588',.NOTDEFINED.); 5 #2826= IFCMEMBER('09J5N7xMHBfQZeQGAEMomB',#42,'Curtain Wall:Curtain_Wall-Exterior_Glazing:8490',$,'Curtain Wall:Curtain_Wall-Exterior_Glazing:8490',#2762,#2823,'294181',.MULLION.); 6 #2972= IFCMEMBER('09J5N7xMHBfQZeQGAEMom8',#42,'Curtain Wall:Curtain_Wall-Exterior_Glazing:8490',$,'Curtain Wall:Curtain_Wall-Exterior_Glazing:8490',#2914,#2969,'294182',.MULLION.); 7 #3063= IFCMEMBER('09J5N7xMHBfQZeQGAEMom9',#42,'Curtain Wall:Curtain_Wall-Exterior_Glazing:8490',$,'Curtain Wall:Curtain_Wall-Exterior_Glazing:8490',#3005,#3060,'294183',.MULLION.); 8 #3115= IFCMEMBER('09J5N7xMHBfQZeQGAEMom7',#42,'Curtain Wall:Curtain_Wall-Exterior_Glazing:8490',$,'Curtain Wall:Curtain_Wall-Exterior_Glazing:8490',#3096,#3112,'294185',.MULLION.); 9 #3167= IFCMEMBER('09J5N7xMHBfQZeQGAEMom4',#42,'Curtain Wall:Curtain_Wall-Exterior_Glazing:8490',$,'Curtain Wall:Curtain_Wall-Exterior_Glazing:8490',#3148,#3164,'294186',.MULLION.); 10 #3219= IFCMEMBER('09J5N7xMHBfQZeQGAEMom5',#42,'Curtain Wall:Curtain_Wall-Exterior_Glazing:8490',$,'Curtain Wall:Curtain_Wall-Exterior_Glazing:8490',#3200,#3216,'294187',.MULLION.); 11 #3279= IFCMEMBER('09J5N7xMHBfQZeQGAEMom3',#42,'Curtain Wall:Curtain_Wall-Exterior_Glazing:8490',$,'Curtain Wall:Curtain_Wall-Exterior_Glazing:8490',#3252,#3276,'294189',.MULLION.); 12 #3339= IFCMEMBER('09J5N7xMHBfQZeQGAEMom0',#42,'Curtain Wall:Curtain_Wall-Exterior_Glazing:8490',$,'Curtain Wall:Curtain_Wall-Exterior_Glazing:8490',#3312,#3336,'294190',.MULLION.); 13 #3447= IFCMEMBER('09J5N7xMHBfQZeQGAEMom1',#42,'Curtain Wall:Curtain_Wall-Exterior_Glazing:8490',$,'Curtain Wall:Curtain_Wall-Exterior_Glazing:8490',#3372,#3444,'294191',.MULLION.); 14 #3555= IFCMEMBER('09J5N7xMHBfQZeQGAEMomU',#42,'Curtain Wall:Curtain_Wall-Exterior_Glazing:8490',$,'Curtain Wall:Curtain_Wall-Exterior_Glazing:8490',#3480,#3552,'294192',.MULLION.); 15 16 #3585= IFCRELAGGREGATES('3cUkl32yn9qRSPuBJVyW_P',#42,$,$,#2375,(#2470,#2628,#2730,#2826,#2972,#3063,#3115,#3167,#3219,#3279,#3339,#3447,#3555));
#3585（IfcRelAggregates）表示聚合关系,#2375幕墙（IfcCurtainWall）是由各个部分#2470, #2628, #2730, #2826, #2972, #3063, #3115, #3167, #3219, #3279, #3339, #3447, #3555组成。
参考链接：https://blog.csdn.net/liyazhen2011/article/details/81664319