Faithfulness of transformation depends on the functional and never on the formal approach to the choice of corresponding linguistic means. E.g.
I wanted to have done it myself. -Я хотів це зробити сам, але не зробив.
The perfect infinitive expresses unaccomplished action; as there are no Ukrainian equivalent form we use lexical means. Thus, equivalence can be best achieved if the translator does not intent to mirror or copy the grammatical forms.
Very often the part of speech changes in translation, it is called substitution or conversion. It's often used because English uses more verbal forms while Ukrainian has more nominal forms: Bionics has many application beyond the field of medicine -Біоніка широко застосовується і поза межами медицини adj → adv, n →v.
Such substitution often cause restructuring of the sentence and changing of word order (permutation).
They have been working on the theory construction for years. -Вони роками працюють над побудовою цієї теорії.
The subject of the sentence may be omitted in Ukrainian-it is called zero transformations. The door will not open - Двері неможливо відчинити -The subject the door is transformed into object.
The combination of two simple sentence is called integration or fusion. The devision of the long sentence into two or more sentence is called partening. Sometimes they are called reduction and extension).
Objectively predetermined are transformations of the passive voice constructions by active voice, of the objective with the infinitive or participle constructions /complexes, gerundial and nominative absolute participle constructions, national idioms. They are grammatical transformations combined with lexical.