The closer comparison to make is between oratorio and Opera. Oratorios were originally created to be the church's response to opera which the 17th century church considered somewhat sinful. Therefore, oratorios are really unstaged operas. As a matter of fact, they can be quite similar musically and there have been a few oratorios that have been staged from time to time. Loosely speaking, a cantata is a short oratorio.
Which of these is a shorter version of an opera or oratorio?
Oratorio
An oratorio does not have acting, scenery, or costumes as an opera does but does have arias, recitatives, chorus, and orchestra.
Oratorio uses sacred text, and is typically not staged (no costumes, lights, sets, etc.).
They are all performed to music.
An oratorio is a large vocal and instrumental dramatic work based on a sacred subject. The main difference between an oratorio and an opera is that an oratorio has no staging or costumes.
Which of these is a shorter version of an opera or oratorio?
Overature
Oratorio
An oratorio does not have acting, scenery, or costumes as an opera does but does have arias, recitatives, chorus, and orchestra.
An oratorio is a large musical composition comprised of an orchestra, a choir and soloists. Similar to an Opera in the story telling, but different in it is just music not singing. Baroque references the time frame of 1600-1750 when the oratorio was written.
Handel's Messiah is an Oratorio, which is basically an opera without a stage. The Messiah is one of the few of Handel's Oratorio's without characters, which leads to the confusion expressed by many people (including yourself). The oratorio itself has a colorful place in music history; Handel's turning to the genre occured after the British public lost taste for his operas.
Oratorio uses sacred text, and is typically not staged (no costumes, lights, sets, etc.).
Yes, you could make an educated guess. Oratorio plots are often based on sacred topics. Opera plots are about murder, romance, etc... Also, the characters in an oratorio have much less interaction with each other than the characters of an opera.
They are all performed to music.
Libretto
An oratorio is just sung using solo voice or choral pieces. The opera uses solos and choral voices too, but involves stage acting as well. For example, Handel's Messiah is an Oratorio ... La Boheme is an Opera.