DEM is a database structure been wrote in JSON format. DEM is designed for distributed development of a project database. DEM can describe whole database or just a part of them. DEM should be used with classic relational DBMS (MariaDB/MySQL, Postgres, ...), it is not for NoSQL DBs.

DEM is like XML mapping in Doctrine or in Hibernate but is focused on database structure only (PHP/Java objects structure is skipped).

{"DEM": {}} 

Every node in DEM is a branch (user, sale) or nested branch (user/group, sale/order).

{
  "DEM": {
    "user": {
      "group": {}
    },
    "sale": {
      "order": {}
    }
  }
}

Path is a chain of branches starting from DEM node. Path in DEM is like a path in filesystem - absolute (starts with '/') or relative (starts with './', '../' or just a name).

• /user
• /user/group
• sale
• ../order

All DEM nodes are branches except . nodes & .comment nodes. . nodes contain main information about database structure. Assignment of this information depends from it placement in the DEM.

Any node named as .comment is a comment string:

{
  "DEM": {
    ".comment": "This is demo DEM.",
    "branch": {
      ".comment": "This is demo branch."
    }
  }
}

. node directly under the DEM is a string and means that described structure should be placed into appropriate branch in common DEM when some DEM structures are merged:

{
  "DEM": {
    ".": "/vendor/module/submodule",
    "customer": {}
  }
}

This DEM will be converted into:

{
  "DEM": {
    "vendor": {
      "module": {
        "submodule": {
          "customer": {}
        }
      }
    }
  }
}

before merge.

DEM[.] always started from root. So

{ "DEM": { ".": "vendor/module/submodule" } }

is equal to

{ "DEM": { ".": "/vendor/module/submodule" } }

We can create many modules with DEMs inside (and with own mounting points), then combine all of them into one DEM structure. This allows us to create a single database from many DEMs.

If DEM[.] is omitted then all branches from this DEM will be mounted into the root.

branch[.] contains information about entity (table). Path to this branch is a table name:

{
  "DEM": {
    ".": "/user",
    "group": {
      ".": {}
    }
  }
}

Entity with name /user/group in DEM corresponds to table with name user_group in DB.

. structure:

".": {
  "desc": "",           // description: been converted to table comment;
  "attr": {},           // attributes: table columns;
  "index": {},          // indexes: unique & search;
  "relation": {}        // relations: foreign keys;
}

. node of a branch contains all information that is needed for table creation. Only branches with . node are converted into tables:

{
  "DEM": {
    ".": "core",
    "user": {
      ".": {},
      "registry": {
        ".": {}
      },
      "group": {
        "acl": {
          ".": {}
        }
      }
    }
  }
}

This means that 3 tables will be created:

• core_user
• core_user_registry
• core_user_group_acl

Entity attribute is a table column. Table column has (Doctrine, Hibernate) own attributes:

• name

• comment

• type

• default

• nullable

• length

• scale

• precision

  { "DEM": { ".": "core", "user": { ".": {

    "attr": {
      "id": {
        "type": "identity",
        "desc": "Eatery ID"
      },
      "name": {
        "type": "string",
        "desc": "Eatery's default name (if not i18n)."
      }
      }
    }
  }
  

  }

Currently these types are available:

• binary
• boolean
• datetime
• decimal
• identity
• integer
• reference
• text

{
  "DEM": {
    ".": "/vendor/module",
    "user": {
      ".": {
        "desc": "User data.",
        "attr": {
          "id": {
            "desc": "Entity ID.",
            "increment": true
          },
          "group_ref": {
            "desc": "User Group reference.",
            "reference": true
          }
        },
        "index": {
        
        },
        "relation": {
          "./group": {
            "own": ["group_ref"],
            "foreign": ["id"],
            "on": {"delete": "restrict", "update": "restrict"}
          }
        }
      },
      "group": {
        ".": {
          "desc": "User Group data.",
          "attr": {
            "id": {
              "desc": "Entity ID.",
              "increment": true
            }
          }
        }
      }
    }
  }
}