Is the whole plain text of a message translated into a unique code?

Question

Suppose that we have a cryptosystem, say $(P,C,K,E,D)$ where $P$ denotes the plain text, $C$ is the cipher text, $K$ is the key space, $E:K\times P\to C$ is the encryption function and $D:K\times C\to P$ is the decryption function. Let's suppose that an agent, who is an investment analyst of a hedge fund, wants to transmit to the stakeholders the information "The strategy of our investment fund is to invest in the portfolio $W$ with estimated mean $\mu=8$ units of payoff and variance $\sigma^2=2$." The whole proposition is a plain text. By making an encryption of this text and transform it to cipher text do we transform the whole proposition to a one unique code, that is represented by a number? For example $E(\text{key},\text{proposition=plain text})=c\quad\text{which is a number}$ which means that the key and the cipher are uniquely associated with the specific proposition and hence $E$, $D$ are some kind of inverse functions one another?