Where to find the information regarding relationships between the tables?

I am developing a Windows based app which among other things let’s users view SAP table schema and relationships.

If I use SAP GUI and dig up a bit on say the MARA table I can see that

Material Master (MARA) is related with

1) MaterialDescription (MAKT) on columns MANDT and MATNR

2) MaterialPlantData (MARC) on columns MANDT and MATNR

and so on…

My question is - in which table the information regarding relationships between the tables is stored? There must be a data dictionary table which would be storing the relationships data. Which is it? Note: I will programatically access the table, NOT from the UI.