The following contents covers a basic overview of the EC API Technology.
Exploring API Technology
Objective
Introduction
Recorded Webinar: Employee Central and OData API Introduction
API Technology Overview
API-First Strategy
The Intelligent Enterprise Framework
OData offers partners and customers a consistent API experience for the Intelligent Enterprise.
- Integrate intelligent technologies into extensions with consistent techniques.
- The same tools and skill sets apply across products.
- Leverage existing assets to quickly execute on the Intelligent Suite vision.
- OData is SAP's architectural standard.

API-First Architectural Vision
External Application to/from SAP SucccessFactors System - Data Replication
- 3rd Party system replicates data from or to a SAP SucccessFactors system
- Usually middleware involved
- Technical users used for replication

External Application to SAP SucccessFactors System real-time - UI integration
- Application access data in real-time from a SAP SucccessFactors system
- Usually Application Platforms involved
- Named user access
Benefits of an API-First Approach
Higher Quality
- APIs are easier, less expensive to test with Automation Framework (AAF v2) and metadata-driven testing
- Widespread use of shared services minimizes chance of test escapes
- API Data and Configuration services are easier to mock for Test Driven Development (TDD)
- UX testing only needs to test Controller logic since underlying services are already tested
Time to Market/Cost of Ownership
- Improves overall time to market for mobile, desktop, partner applications, custom applications
- GDPR, CypherCloud, encryption and other features easier to implement with a central set of services on a common framework
- No dual maintenance - only a single set of business logic is maintained.
- Functional improvements benefit all applications
Scalability/Stability
- Mediate, monitor, analyze and throttle API via SAP API Management in our data centers
- API performance improvements benefit all applications
- APIs are essential for any microservice architecture
Available API/Integration Technologies for EC
Integration/API Evolution
Import/Export: CSV File (automation via FTP possible)
SOAP APIs
- Compound Employee: Specialized SOAP service for data replication (read-only)
OData APIs
- EC OData read APIs for UI consumption and replication
- EC OData upsert APIs for data replication
- MDF OData read/write APIs for UI consumption and replication
Employee based - Compound Employee API
Employee based - Compound Employee API - I
Compound Employee

Back to the Entity Relation Diagram, it shows the Compound Employee API includes a set of entities which are surrounded by orange line. Compound Employee API is a kind of EC SOAP API technology and it focused on replication employee master data from Employee Central.
Employee based - Compound Employee API - II
Request:

Response:

If we query Compound Employee, the query clause is no longer fields but the entities name (person, personal_information) which compared with SAP SuccessFactors direct API.
Employee based - EC OData API - I
EC OData APIs using navigations incl. MDF

OData APIs supports navigation for associated entities, it automatically creates navigations from the source entity to the target entities, based on the relationship defined. Navigations in an entity represent associations between entities. Each entity can have the following properties.
- Effective dating
- Business keys
- Required / nullable attribute
- Processing parameters for upsert
Employee based - EC OData API - II
Look at this API request and response, we can easily extend existing Employee Central (EC) entities (personalInfoNav) by using expand functionality and build EC customer extensions for partners and customers. MDF allows you to customize customer objects and related application logic as needed to meet your client's needs.
Request:
https://salesdemo4.successfactors.com:443/odata/v2/PerPerson?$format=json &$select=personIdExternal,dateOfBirth, personalInfoNav/startDate, personalInfoNav/firstName, personalInfoNav/lastName, personalInfoNav/customString1&$expand=personalInfoNav &$filter=personIdExternal%20eq%20'greinhard3‘
Response:

Your options and reasons when to choose which one
When to use imports/export…
- For initial data load or if you are not able to consume APIs (SOAP or OData).
When to use OData and when SOAP…
- If you want to make use of RBP and concurrent user access to build own UIs on top of EC using an extension platform OData is the technology of your choice.
- If you want to access MDF Data OData is the only technology of choice.
- For data replication using a technical user (read or write) both SOAP and OData can be used, but we recommend to use OData since OData has a better coverage of entities.
When to use SOAP Compound API…
- If you require for employee replication field level delta, snapshot or read modified employees only.
- If you require to read employee master data only (CE does not support write).
SAP Help Documentation
Solution Highlights
OData:
- Standardized API following the OData V2 specification
- Custom Configurable objects come with CRUD OData APIs
- OData APIs react to data model changes
- OData APIs allow navigation through the data model using $expand
- Target technology for both integration and UI use cases
- User based authorization support
- oAuth and Basic authentication possible
SOAP API:
- Employee Central offers for Employee Data replication a powerful SOAP interface (read-only)
- Several modes available such as full transmission, delta, period delta and snapshot
- Optimized for high data loads
More Information:
Deprecated Technology
SOAP Interface
- All AdHoc Reports
- PerDirectDeposit
- Compound Employee - All direct SFAPI from August 2018
File based Imports
- PerDirectDeposit