What does the 2 type LSA do? There are no 2 types of LSA that cannot build a topology?

This question also puzzled me for a long time, a lot of various IE also can't answer up.

There are no 2 types of LSA, and I have experimented with topologies that can be drawn according to the 1 class LSA .

But one thing is missing: The description of the link is bidirectional. Take point-to-point, two routers will say I connect to you, you connect to me, as follows the first class is point-to.

           First Class link point to point    link                      1.Link -id   Neighbor's router-id                      2.Link-type   Point to Point                      3.Link-data   this router's interface on this link ip            Class II link  stub network  link                        1.Link-id       Network Address                        2.link-type   stub network                          3.Link-data    Subnet Mask             Category III link  transmit  network  link                       1.Link-id    in the network segment interface                         2.Link-type  Transmit  network                          3.Link-data    interface of this link               Fourth Class link   Virtual-link   link                                1.Link-id     Neighbor router-id                       2.Link-type   virtual-link                       3.Link-data   interface IP for physical port used by virtual link

However, in the MA network of OSPF, each router and Dr Establish a neighbor, Dr is actually a virtual device, such as Dr is R2, but R2 will also say I connect to the DR,

Then Dr needs to describe himself connected to which routers, two-way establishment, if a router a description, certainly unscientific, then directly produces a 2 class LSA. It contains all the router-id of this network, plus a mask.

What does the 2 type LSA do? There are no 2 types of LSA that cannot build a topology?