I want to know if there is any shortcoming that ABE cannot achieve and that the ABS complete it. I mean why the ABS is included if the authentication and the authorization are already ensured by the ABE. I really need to know the real utility of the ABS and what it brings in more compared to the ABE.
Attribute-Based Encryption (ABE) schemes are a way to securely send (i.e share) a plaintext (message) amongst some particular receivers. The data owner (sender) consider an access policy to encrypt the message under this policy that a data user (receiver) is able to decrypt the ciphertext if and only if he/she satisfies the policy. So the ABE schemes just provide the confidentiality for a sensitive data because all certified users are able to calculate the ciphertext corresponding a particular policy (the data owner secret key is not an input for encryption algorithm).
In this point, the Attribute Based signature (ABS) schemes should be considered to achieve authenticity. In these schemes, the data owner who has a bunch of secret keys corresponding to his/her attributes wants to convince the other users about this claim (I am a person with some specific features, for instance, I am "Tall", "Male" and so on). The receiver authenticates this claim if and only if the signature which is produced by the sender based on her/his secret keys satisfy the published access policy with the plain message. In the other word, if the verification algorithm runs correctly then the conditions will be passed.
Overall, in the former schemes, the secret key condition is on the receiver side while the latter focus on the sender side to ensure the secret key corresponding the claimed attributes.
Also, the Attribute-Based Singcryption (ABSC) schemes follow the same target and satisfy not only the authentication but also the confidentiality properties. Precisely, ABSC schemes are the merge of ABE and ABS while are more efficient than executing both ABE and ABS, separately. [https://eprint.iacr.org/2018/263.pdf]