We first demonstrate the approach through a simple example, and then propose a structure of system artifacts based on formal levels of abstraction.

首先，我们会通过一个简单的示例演示此方法，然后提出一个基于正式抽象层次的系统产品的结构。

youdao

All languages have two general levels of usage—a formal level and an informal level.

所有语言都有两种基本的用法——正式用法和通俗用法。

youdao

Finally, we found that the presence of a friendly, but not knowledgeable, mediator can enable children to reach levels of learning similar to formal schools with trained teachers.

最后，我们发现，一种友好但不博学的媒介，可以使孩子们达到类似于在有训练有素教师的正规学校的学习水平。

youdao

The event will create dialogue between young people, policy-makers, practitioners and researchers to promote meaningful youth engagement within different levels of formal and non-formal education and training sectors.

UNESCO: Detailview | United Nations Educational, Scientific and Cultural Organization

Promote and use OER to widen access to education at all levels, both formal and non-formal, in a perspective of lifelong learning, thus contributing to social inclusion, gender equity and special needs education.

UNESCO: 2012 PARIS OER DECLARATION

How is it that colonists in the 1770s, many of whom had little formal schooling, had higher levels of literacy, more expansive vocabularies and a better command and mastery of a wide variety of subjects, than the average student today?

FORBES: The Un-Education of a Nation: Where We Went Wrong