Sonata的曲式有何特點？

Sonata is a form of a piece 'discovered' in the classical era by Joseph Haydn. A standard sonata is divided into 3 parts: Exposition, Development and Recapitulation

The main theme of the sonata will be first heard in exposition, in the home key. the first theme will be ended in the dominant key of the own key. It is possible to have a 2nd theme in the exposition but in the dominant key. In between themes it is possible to have a transition to link up both themes.
Development will be a part to develop themes sounded in exposition, but it wont be in the home key...it could be in minor but uses the elements sounded (for example rhythmic motive). Like if the theme used in the development was first sounded in C major, in the development it could be sounded in a minor instead.
Recapitulation is the part after development. everything in this section will be in the home key. The first theme of the piece will be sounded again here to indicate the return of the recap. 2nd theme will be sounded as well but in the home key instead of in the relative keys.
Sometimes there will be coda following the development, and to have the home key sounded again like a grand ending of the piece.
Sonata is not a genre only for classical era but it was discovered in the classical era, usually for one solo instrument (not including accompaniment if available) In the later music historical period the form of sonata is not only 3 main parts but the skeleton of the sonata is still 3 main parts.