# Basic Concepts#

This chapter introduces the basic terminologies you will encounter in the docs. But first, let’s look at the code below:

from jina import DocumentArray, Executor, Flow, requests

class FooExec(Executor):
@requests
async def add_text(self, docs: DocumentArray, **kwargs):
for d in docs:
d.text += 'hello, world!'

class BarExec(Executor):
@requests
async def add_text(self, docs: DocumentArray, **kwargs):
for d in docs:
d.text += 'goodbye!'

with f:
f.block()

from jina import Client, DocumentArray

c = Client(port=12345)
r = c.post('/', DocumentArray.empty(2))
print(r.texts)


Running it gives you:

['hello, world!goodbye!', 'hello, world!goodbye!']


What happens underneath is depicted in the following animation:

The following concepts will be covered in the user guide:

Document#

Document is the fundamental data structure in Jina for representing multi-modal and cross-modal data. It is the essential element of IO in Jina. More information can be found in DocArray’s Docs.

DocumentArray#

DocumentArray is a list-like container of multiple Documents. More information can be found in DocArray’s Docs.

Executor #

Executor is a Python class that has a group of functions using DocumentArray as IO. Loosely speaking, each Executor is a microservice.

Flow#

Flow ties multiple Executors together into a logic pipeline to achieve a task. If Executor is a microservice, then Flow is the end-to-end service.

Gateway#

Gateway is the entrypoint of a Flow. It exposes multiple protocols for external communications; it routes all internal traffics.

Client#

Client is for connecting to a Gateway and sending/receiving data from it.

Deployment#

Deployment is an abstraction around Executor that lets the Gateway communicate with an Executor. It encapsulates and abstracts internal replication details.

gRPC, Websocket, HTTP#

They are network protocols for transmitting data. gRPC is always used between Gateway and Deployment communication.

TLS#

TLS is a security protocol designed to facilitate privacy and data security for communications over the Internet. The communication between Client and Gateway is protected by TLS.

## Relationship between Jina and DocArray#

DocArray is a crucial upstream dependency of Jina. It is the data structure behind Jina. Without DocArray, Jina can not run.

DocArray contains a set of rich API for on the local & monolith development. Jina scales DocArray to the cloud. The picture below shows their relationship.

In a common development journey, a brand-new project first moves horizontally left with DocArray, leveraging all machine learning stacks to improve quality and completing logics in a local environment. At this point, a POC is built. Then move vertically up with Jina, enhancing the POC with service endpoint, scalability and cloud-native features. Finally, you reach to the point where your service is ready for production.